The safety and tolerability of carvedilol, a new antihypertensive agent with the combined pharmacological activities of beta-blockade and vasodilation, and of nifedipine were investigated in patients with essential hypertension and non-insulin-dependent (type II) diabetes mellitus. Twenty patients were openly randomized to receive 25 mg carvedilol once daily (five men and five women; mean age, 63 years) or 10 mg nifedipine t.i.d. (three men and seven women; mean age, 64 years) for a period of 4 weeks. Baseline mean sitting blood pressures were 168/98 and 169/95 mm Hg in the carvedilol and nifedipine groups, respectively. Baseline mean areas under the curve (AUC) of the intravenous glucose tolerance test (IVGTT) for the carvedilol and nifedipine groups were 6,136 +/- 1,195 and 6,287 +/- 1,228 mg/dl/min, respectively. Demographic and efficacy variables were not statistically different between treatment groups. After 4 weeks of therapy, mean sitting blood pressure was significantly (p less than 0.02) reduced to 144/91 mm Hg in the carvedilol group and to 149/87 mm Hg in the nifedipine group. Week 4 IVGTT AUC values of 5,735 +/- 1,464 mg/dl/min in the carvedilol group and 5,988 +/- 993 mg/dl/min in the nifedipine group, representing mean reductions of 6.14% and 3.17%, respectively, were not statistically different from baseline. Both treatments were well tolerated. No patient experienced adverse events in the carvedilol treatment group, whereas two patients in the nifedipine group reported episodes of headache (one patient) and palpitations (one patient); each episode was mild in severity and considered to be related to study medication.(ABSTRACT TRUNCATED AT 250 WORDS)