Hand tremor, heart rate, and electrolyte, plasma (pl) insulin, blood (bl) glucose, and pl terbutaline levels were measured in 11 healthy men during infusion and oral administration of terbutaline. Infusion of terbutaline (250 micrograms) was followed by increases in pl insulin concentration and bl glucose and by a decrease in pl K. Similar metabolic changes were seen on day 1 of oral terbutaline (5 mg x 3). Heart rate was moderately increased by terbutaline over the entire period (13 days) or oral dosing. Hand tremor always increased after terbutaline, but to a lesser degree on days 4 and 13 than after the first oral dose. On day 13 there was a very small increase in pl insulin and no reduction in pl K; bl glucose increased slightly from an elevated basal level. Pl terbutaline was of similar maximum concentrations on days 1 and 13, indicating that the tolerance was mediated through reduced response of the effector organs.