OBJECTIVE: We examined the effect of diazoxide, an ATP-sensitive K(+) channel opener and inhibitor of insulin secretion, on beta-cell function and remission in children at clinical onset of type 1 diabetes. RESEARCH DESIGN AND METHODS: A total of 56 subjects (21 girls and 35 boys, age 7-17 years) were randomized to 3 months of active treatment (diazoxide 5-7.5 mg/kg in divided doses) or placebo in addition to multiple daily insulin injections and were followed for 2 years. RESULTS: Diazoxide decreased circulating C-peptide concentrations by approximately 50%. After cessation of the treatment, basal and meal-stimulated C-peptide concentrations increased to a maximum at 6 months, followed by a decline. Meal-stimulated C-peptide concentration was significantly higher at 12 months (0.43 +/- 0.22 vs. 0.31 +/- 0.26 nmol/l, P = 0.018) and tended to fall less from clinical onset to 24 months in the diazoxide- vs. placebo-treated patients (-0.05 +/- 0.24 vs. -0.18 +/- 0.26 nmol/l, P = 0.064). At 24 months, the meal-stimulated C-peptide concentrations were 0.24 +/- 0.20 and 0.20 +/- 0.17 nmol/l, respectively. Side effects of diazoxide were prevalent. CONCLUSIONS: This study demonstrates that partial inhibition of insulin secretion for 3 months at onset of childhood type 1 diabetes suspends the period of remission and temporarily preserves residual insulin production. Further evaluation of the full potential of beta-cell rest will require compounds with less side effects as well as protocols optimized for sustained secretory arrest.