The concept that viral infections of the mother during gestation may adversely affect the developing young had been accepted with considerable reluctance until the papers by Gregg1and Swan * appeared. Since Gregg's report in 1942 on the frequency of abnormalities in children born of women who had contracted rubella during early pregnancy, there have been many confirming reports. Surprisingly little evidence has turned up in the past 10 years, however, to incriminate other diseases as causing abnormalities when they infect the mother early in pregnancy. There are several possible explanations for this fact. First, most of the easily diagnosed virus diseases, such as rubeola, mumps, and chicken pox, occur as a rule in childhood before the normal child-bearing period. Most of these diseases confer immunity, and consequently the incidence of their occurrence in young adults is rather rare. Rubella, on the other hand, does not appear to confer solid