Recent data suggests that one of the major actions of sulfonylureas is to potentiate the anabolic cellular effects of insulin. This is the first study to examine the use of sulfonylureas as adjunctive therapy in newly-diagnosed type I diabetic children. A random, prospective, double blind study over 15 months, stratified by age at diagnosis, was conducted. The treatment group (n = 13) received daily oral weight-adjusted tolazamide whereas the control group (n = 11) received placebo. Monthly comparison of the HbA1 values between groups revealed no statistical difference; likewise, the fasting serum C-peptide values were not dissimilar. The mean daily insulin dose per kilogram, however, was less in the tolazamide group (P less than 0.001). The data suggests that the addition of tolazamide may not be of therapeutic benefit in newly diagnosed juvenile diabetics, although insulin requirements may be reduced.