Using the nationwide childhood-onset diabetes register in Sweden, we were able to trace children who contracted diabetes before the age of 15 years and who were born at a specific hospital in Sweden where maternal sera from delivery had been stored during the years 1969-1989. Sera obtained at delivery from 57 mothers of diabetic children were compared with sera from 203 mothers of control subjects who were delivered at the same hospital during the same time period. The sera were analyzed blindly using a group-specific enzyme-linked immunosorbent assay for enteroviral IgG and IgM antibodies before and after urea wash as an avidity test. On the same plates, IgG antibodies to herpes, mumps, and toxoplasmosis were analyzed. The mean absorbance values of enteroviral IgG antibodies against enteroviral antigens (echo30, coxsackie B5, and echo9) were significantly higher among mothers whose children later developed diabetes (P = 0.002, P = 0.02, and P = 0.04, respectively). When reduction in activity after urea wash, indicating recently formed antibodies, was compared, the differences were even more pronounced (P < 0.001 for all three antigens). No significant differences were found for antibodies against herpes (all types), herpes type 2, mumps, or toxoplasmosis. When IgM activity and/or a significant decrease in avidity index, an indication of recent enterovirus infection, was used as a risk exposure, the odds ratio standardized for year of birth (95% confidence interval) was 3.19 (1.39-7.30). We conclude that the results of this study indicate that enteroviral infection during pregnancy is a risk factor for childhood-onset diabetes in the offspring.(ABSTRACT TRUNCATED AT 250 WORDS)