Several recent reports have linked the administration of beta-adrenergic agents to the development of hypokalemia. This led us to study, under controlled conditions, the effects of a subcutaneous injection of 0.25 mg terbutaline sulfate on serum potassium (K+), sodium (Na+), glucose, and insulin in a group of asymptomatic asthmatics. Heart rate (HR), blood pressure (BP), and forced expiratory volume in one second (FEV) were measured as parameters of beta-adrenergic stimulation. Each of 7 subjects was studied on 2 separate mornings after an overnight fast. Measurements were obtained before and at various time intervals after 0.25 mg) of terbutaline sulfate or 0.25 ml of a normal saline solution (placebo) were injected subcutaneously in a double-blind randomized crossover fashion. Terbutaline injection significantly increased HR and FEV and lowered diastolic BP for a period in excess of 3 h, indicating a prolonged beta stimulatory action of the drug. Significant effects on glucose, K+, and insulin were observed as early as 15 min after terbutaline injection; serum glucose and insulin increased and remained elevated for at least 2 h. Serum K+ fell significantly, reached a peak decline of 14% from the control value at 30 min after the injection and remained decreased for a period in excess of after subcutaneous terbutaline injection should be interpreted in the light of these effects of the drug and that terbutaline should be used with caution in patients prone to hypokalemia.