In 1948 Lila and Ella Wigren proved that pop art imitates nature. They were a couple of 17-year-old happy hoofers in the chorus line at Chicago's Chez Paree, just out of high school and down from the Finnish community of Ludington, Mich. to seek their show-biz fortunes.

They were also identical twins, and when an executive of the Toni home permanent company saw their act one night, the twin Finns were "jammed in a cab" (recalls Ella) and whisked off to a photo studio. There they were camera-tested for a new ad campaign called "Which Twin Has the Toni?" Soon the Wigrens became one of 16 sets of twins to defy the public to distinguish between the cut-rate home hairdo and the professionally done coiffure.

For four years the curly-topped twins appeared in magazines, on billboards and in department stores, and then both decided to get married, Ella eloping 48 hours before Lila's church wedding. They remained close but changed their hairdos and stopped dressing alike. People rarely asked, "Which twin are you?" Lila married Larry Malecki, an industrial equipment salesman, and had three daughters. Ella, whose husband, Ed Drath, works for a marking-systems company, had two. The sisters disappeared for two decades into the quiet suburban world of Arlington Heights, Ill.

A few months ago they read about research being conducted at the University of Indiana's Genetics Center in conjunction with the National Institutes of Health. Two doctors, Joe C. Christian and Walter Nance, were collecting data on more than 4,000 families that might have genetically related diseases—with particular emphasis on whether high blood cholesterol in twins is inherited or influenced by environment. The twins volunteered as statistical guinea pigs and underwent extensive medical testing and interviewing.

They had a reason. "Our father passed away from a stroke and our mother died in 1969 from heart disease," explained Lila, "and our eldest sister Helen was a blue baby born with heart disease. We were afraid it was hereditary and we hoped none of our children would be affected."

After the tests Lila and Ella learned the good news: data so far indicated a high blood cholesterol level is not hereditary and therefore cannot be passed on to offspring. The study also showed that children of identical twins are, at least genetically, half-siblings—much more like sisters than cousins. Lila and Ella have become aware that their daughters often talk and act alike and have similar interests and talents—just as the twins did as children.

Lila and Ella have discovered that they are truly two peas in a pod. "A member of the test team told us that our bone structure and fingerprints are so similar that we could be one person. Our blood pressure, cardiogram, cholesterol level—everything is the same." The tests have had one unexpected side effect: the two women have begun dressing alike again and wear their hair in identical frizzes. Which brings up the question: which twin actually did have the Toni? Turns out it was Ella all the time.