The efficacy and tolerability of controlled-release metoprolol (metoprolol CR/ZOK), 100-200 mg, and atenolol, 50-100 mg, once daily was compared in Chinese patients with mild to moderate essential hypertension. The study was of a randomized, double-blind, two-way crossover design. The active treatment periods lasted 4 weeks each and were preceded by a 4-week placebo run-in period. The two double-blind phases were separated by a 2-week washout period on placebo. Blood pressures and heart rates were measured at rest in each 2-week visit and during exercise at the end of each treatment period. Twenty-four patients (M/F = 14/10) were valid for efficacy analysis. Their ages ranged from 39 to 68, with a mean of 53.5 years. The rest supine blood pressure and heart rate before active treatment was 160 +/- 15/106 +/- 6 mmHg and 75 +/- 14 beats/min (mean +/- SD), respectively. A responder was defined as exhibiting a supine diastolic blood pressure < or = 90 mmHg or a supine diastolic blood pressure reduction of at least 10% of the baseline level. Both agents had high response rate: 88% and 92% of all patients responded to metoprolol CR/ZOK and atenolol, respectively. Both active treatments considerably reduced resting systolic and diastolic blood pressures and heart rates as compared with baseline (p < 0.001), respectively. With controlled-release metoprolol, a more pronounced beta 1 blockade was obtained than with atenolol, which was expressed as a significant reduction in exercise-induced heart rate at the highest comparable workload compared with placebo (p < 0.05). These findings are compatible with those reported from western populations.