The efficacy of the calcium channel blocker nitrendipine in preventing early renal and glomerular hypertrophy and increased urinary albumin excretion (UAE) was studied in experimental diabetes in rats, starting treatment at the onset of diabetes. Female Wistar rats were randomised into four groups: diabetic and non-diabetic rats were given either placebo or nitrendipine (250 mg/kg) in the diet for 8 weeks. After 8 weeks the kidneys in the diabetic animals had increased significantly compared to the non-diabetic controls. In the diabetic nitrendipine-treated animals renal and glomerular hypertrophy was significantly smaller than in the diabetic placebo-treated group (p < 0.05). After an initial increment within the first week, the UAE remained constant throughout the study period in the diabetic nitrendipine-treated animals, while a steady increase was seen in the diabetic placebo-treated group (p < 0.05). No differences were seen in systemic blood pressure between calcium- channel-blocker-treated groups and placebo-treated groups. In conclusion, administration of nitrendipine to diabetic rats for 8 weeks had a significant inhibitory effect on renal and glomerular hypertrophy, and showed a tendency towards a reduction in UAE (p = 0. 06) without affecting metabolic control or systemic blood pressure.