The possibility that respiratory muscle function may be improved by drug therapy is of clinical importance, but remains controversial. A series of studies concerning the effects of maximally tolerated dosages of terbutaline, tulobuterol (a new beta 2-agonist) and caffeine on respiratory muscle strength and limb muscle strength and endurance were undertaken in normal subjects. Drugs were administered orally, 2 h before study. Caffeine produced a small but statistically significant increase in the stimulated contraction force at 20 Hz, and a small beneficial effect on recovery from a fatiguing protocol; maximum voluntary contraction force of the quadriceps was increased by 3.8%. Terbutaline and tulobuterol had no beneficial effects on either respiratory or limb muscle function. We conclude that conventional dosages of these bronchodilator drugs do not greatly affect skeletal muscle performance.