Human lymphocyte antigen (HLA)-DR-typing was performed in 117 insulin-dependent diabetics with age at onset between 0.5 and 17 years (mean ± SD, 9.0 ± 3.9); 115 of 117 patients were DR3- and/or DR4-posirive. DR4 was very common, seen alone or in combination with other DR types in 82.9% of the patients. Only two children were DR2-positive, but they also were DR4-positive. A comparison between DR3 and DR4 patients snowed that DR4 patients manifested a seasonal variation of onset (most common onset during spring and autumn), had more severe signs and symptoms of the disease at onset, and were less likely to have a partial remission than patients with DR3. The results support the hypothesis that insulindependent diabetes mellitus is a genetically heterogeneous disease.