The effect of vasodilation (with nifedipine) or beta-adrenergic receptor blockade (with propranolol, alprenolol or metoprolol) on the rate of rise of oxygen uptake and heart rate were studied in 14 healthy subjects after a step-wise increase of workload from a light to a moderate exercise intensity. Under beta-adrenergic receptor blockade steady state oxygen uptake at both workload levels was equal to control values; heart rate went up to 111 min-1 (s.d.:15) vs 150 min-1 (s.d.:24) for the control experiments. The half-times of the oxygen uptake transient were unchanged. After vasodilation with nifedipine heart rates were higher (20% for the lower and 12% for the higher exercise level) but steady state oxygen uptake levels and rate of rise were also unchanged. It is concluded that the rate of rise of oxygen supply to working skeletal muscles after a stepwise increase of load is not reduced either by a beta-adrenergic receptor blocking drug nor by a vasodilating agent. Discomfort during exercise appears to be a subjective phenomenon related to reduced skin circulation and sweating under beta-adrenergic receptor blockade, or to headache and congestion after vasodilatory drug administration. These side-effects are not caused by a reduced oxygen supply of muscle, neither under steady state situations nor under rapid changing workload conditions.