We report on the first pilot study in newly diabetic children treated with cyclosporin A (CsA), for 6 months. Three groups of children were recruited based on the desired CsA plasma level: group I (n = 13) aiming at 100 ng CsA/ml plasma; group II (n = 14) at 200 ng/ml, and group III (n = 13) aiming initially at 200 ng/ml and later on 100 ng/ml. These groups were compared to a control group (n = 12) receiving no CsA but the same insulin regimen. A significant reduction in insulin requirements was observed in the CsA-treated children, more marked in groups II and III (p < 0.001 vs. control group). The rate of total remissions was 0 in the control group, and 30% in group I; it was 57 and 76% in groups II and III, respectively. CsA also induced an increase in C-peptide secretion after 6 months (p < 0.01 in groups II and III vs. controls). Side effects of the drug were of minor clinical importance in group I. But in groups II and III, 48% of the children exhibited a reversible increase in blood pressure or plasma creatinine. This study demonstrates a dose-related effect of cyclosporin A (CsA) on the insulin requirements of newly diagnosed diabetic children (more frequent and prolonged remissions with the high CsA dosage). Nevertheless, the noticeable side effects, induced by this high dosage, are of concern for prolonged CsA administration in diabetic children.