The aim of our study was to compare the effect of captopril — the angiotensin-converting enzyme inhibitor, nifedipine — the calcium antagonist, and prazosin — the alpha blocker, on the secretory function of pancreatic β-cells in hypertensive patients with NIDDM and with normal glucose tolerance. The effect of a 2-week treatment with nifedipine, captopril and prazosin upon glycaemia, serum insulin (IRI) and C-peptide (CP) following oral and intravenous glucose load were investigated in three groups, each including 10 non-diabetic patients with essential hypertension (h) and 10 hypertensive type 2 (non-insulin-dependent) diabetics (h + d), aged 32–63 years. Nifedipine produced increase in glycaemia in the oral test in both groups. In the (h) group, but not in the (h + d) group, the drug caused reduction of the glucose-dependent increases in serum IRI and CP, more marked with respect to CP, as expressed by the decrease in the molar serum CP IRI ratio. These results indicate that in non-diabetic patients, nifedipine reduces the early response of β-cells to glucose, but this effect is partly compensated by a decreased insulin uptake by the liver. In patients with type 2 diabetes, this phenomenon does not become manifest because of absence or reduction in the early glucose-dependent insulin release. After captopril, lower values of glycaemia and serum IRI and CP were observed in both groups suggesting an improvement of insulin sensitivity. In conclusion, nifedipine has a small influence, and captopril and prazosin are devoided of any influence on the secretory function of pancreatic β-cells. These drugs may be recommended for the treatment of hypertension in patients with type 2 (non-insulin-dependent) diabetes.