The effects of nifedipine, verapamil and diltiazem on K(+)-induced contraction were investigated in isolated aortic rings from diabetic and age-matched control rats. Six weeks after streptozotocin injection there was no significant difference between the maximum isometric contraction to KCl (80 mmol/l), when expressed per milligram tissue weight, in aortic rings from diabetic rats and those from controls. A concentration-dependent inhibition of the K(+)-induced contraction was observed for the three Ca antagonists in aortic rings from both diabetic and age-matched control rats. Notably, the K(+)-induced contraction in aortic preparations from diabetic rats was more sensitive to nifedipine compared to control preparations (pD2: 8.61 vs. 8.31, p < 0.05), while no significant change in sensitivity towards verapamil (pD2: 6.99 vs. 6.92, p > 0.05) or diltiazem (pD2: 6.33 vs. 6.28, p > 0.05) could be demonstrated. Our data indicate a greater interference of nifedipine with voltage-operated channels in diabetic aortas compared with controls. Since a similar antispasmodic activity was found for diltiazem and verapamil it might be specific for dihydropyridine Ca antagonists.