For the past five seasons, Nicholas Brendon has been known for his sharp one-liners as the demon-hunter Xander Harris on UPN's Buffy the Vampire Slayer. In real life, though, snappy repartee has never been easy for the 30-year-old actor. Since childhood, his speech has been marked by the awkward fits and starts of stuttering.

Researchers say heredity may play a role in the communication disorder, which affects more than 3 million Americans, but its precise cause is elusive. Stress can be a trigger, but not everyone who stutters is a nervous person. "One of the biggest misconceptions is that stutterers are anxious or psychologically different," says Dr. Lisa Scott Trautman, vice president for education of the Stuttering Foundation of America, a nonprofit group that raises money for research and provides information for sufferers. "Another is that people who stutter don't enjoy talking or don't know what they want to say."

Beyond stuttering's physical manifestations are its emotional repercussions. Growing up in Los Angeles as the son of talent agent Kathy and business consultant Bob, both 53, "I felt somewhat isolated. I didn't know anyone else who stuttered," says Brendon, whose identical twin brother Kelly was not afflicted. But today, after years of working to improve his speech, Brendon, who is married to actress Tressa diFiglia Brendon, 30, not only has a thriving acting career but in May became the official spokesman for the Stuttering Foundation. At his Hollywood home, he spoke with correspondent Cynthia Wang about his struggles to overcome the disorder.

I was 7 or 8 when it first started. I don't know why it came on, if I was a stressed-out kid or what. My theory is that being a twin had a lot to do with it. My brother and I always got the same things at Christmas, and you wanted to be the first one to open the present so you would be surprised. It became the same with talking—the fear of not getting it out first. I started to talk really, really fast, so that didn't help.

Kids can be really mean about stuttering. I knew that people didn't really have the patience for it, but my friends were all cool about it. I was always very athletic, so no one cared. But when I went to a new school, finding new friends was a bit harder. My brother Kelly always understood about my stuttering. If I called directory information and couldn't talk, I'd give him the phone and he would talk for me.

When you stutter, you know the word but you just can't say it. Something in your brain holds you up. So you say four or five words for the one you can't say. It breeds frustration and insecurity. You think, "Why do I have these obstacles?"

I took my first speech-therapy class in sixth grade. I had to go to a classroom in a trailer next to my school and do tongue twisters, like "A big black bug bit a big black bear." But in junior high I got an awesome speech teacher. He was the sweetest guy in the world. He taught me vocal exercises, but what I remember most is his incredibly calming presence. It was great to have someone patient enough to listen to you.

By the time I met my wife three years ago, I had conquered a lot of my fears about talking, and it wasn't so much about stuttering as falling in love. But in high school, approaching girls and dating was nonexistent. Instead I got into baseball so I didn't have to talk much. I thought I might play professionally, but at 20 I lost the passion for it. At that time my parents were going through a divorce, and I had pretty much faded out of classes at Pasadena City College and was waiting tables. I thought, "You've got to decide what you want to do with your life." Since I had always been afraid to talk in front of people, I thought acting would be a really big challenge.

I decided to take an acting class, which was really nerve-racking. I would get nervous just getting in the car to drive there, knowing I would have to go onstage. There's a lot of competition, but the challenge really helped me. You're afraid to stutter in front of all those people judging you, so my speech improved because I learned to concentrate more. I learned discipline. When I started looking for acting jobs, I never told anyone about my stutter, and I managed to control it during auditions.

I acted for about two years, did a couple of commercials and then quit because I would stutter on a job from time to time, and it was frustrating. It was just a little hesitation in my speech, the kind of thing no one else would notice, but I did. I wound up doing odd jobs for three years—electrician's assistant, restaurant work. Then at 25 I said, "All right, I've had enough." I went back into acting with a lot of pep talks to myself: "There's no reason why you can't do this." Four months later I was at the right place at the right time, did the best audition I could and was hired for Buffy. I was stoked. I couldn't believe I'd been hired to be a lead in a real TV show.

Acting isn't easy, especially when you're the guy on the show who's got the jokey one-liners. But on-camera, you want to show off. I get adrenaline, and instead of telling my brain to stutter, it makes me more aware, and then I have fun.

For the first two years I was really hard on myself when I messed up. I wanted to be perfect. Now I enjoy performing. And if it takes seven takes to get a scene right, I just do it. There are still times when I start stuttering while playing Xander, but it hasn't been an issue on the show. I just have to say to myself, "Uh-oh, Nick, you're doing it."

Until recently, I hadn't spoken about my stuttering in public. But last year on my birthday, some fans started an official Web site for me, and somehow they found out. The director of the site asked for donations for the Stuttering Foundation. Later the foundation asked if I wanted to be its spokesperson. I wanted to do it for sure.

As a result I've read a lot of letters from people thanking me for speaking up, and it takes me back to the time when things were more challenging for me. I hope my story inspires people. In the meantime I'm getting a book of tongue twisters just to stay in practice. I want to go over them off the set because it really does loosen me up. It's a good way to work out. Especially when you make your money by talking.