Fourteen male physical education students performed a single bout of running until exhaustion on the treadmill at 22 km/h and 7.5% slope. They received single oral doses of 100 mg bupranolol (nonselective beta-blockade), 100 mg metoprolol (beta-1-selective blockade), and placebo 60-90 min before running. Arterialized capillary blood was sampled repeatedly until 30 min after exercise for assessment of lactate and glucose. Adrenaline and noradrenaline were determined in venous plasma before and immediately after exercise. Running time until exhaustion was 49.3 +/- 2.3 s in the control experiment, 44.5 +/- 2.0 s with metoprolol, and 42.7 +/- 2.0 s with bupranolol. The reductions under beta-blockade were statistically significant. With both beta-blockers the increases of the lactate and glucose blood levels were significantly reduced, the levels being almost identical with metoprolol and bupranolol. The post-exercise levels of adrenaline and noradrenaline did not differ significantly between the control, metoprolol, and bupranolol experiments. It is concluded that determination of the lactate and glucose levels in blood did not allow assessment of the mechanism by which beta-blockade impairs the capacity for supramaximal exercise. Besides reduced anaerobic energy release due to inhibition of glycogenolysis, other beta-blocker effects are considered.