Salbutamol infusion was used to study the molecular basis for reduced catecholamine responsiveness in a group of elderly hospitalized individuals. Salbutamol-induced plasma cyclic 3',5'-adenosine monophosphate (cyclic AMP) rise in a group of 10 elderly (mean age 77 years) patients, 8 of whom were hospitalized 6 to 8 weeks after femoral fracture, and 10 younger (mean age 27 years) individuals was compared. Parallel clinical response was monitored by changes in pulse rate and blood pressure. In the younger group there was a three-fold increase in plasma cyclic AMP levels after salbutamol infusion. In the older adults only a one-and-one-half-fold rise in plasma cyclic AMP levels was observed. There was an increase in pulse rate and systolic blood pressure and a decrease in diastolic blood pressure in the younger group compared with the older participants. These results suggest that the basis for reduced catecholamine responsiveness in elderly hospitalized individuals is due to a defect in the peripheral beta-receptor-linked adenylate cyclase complex.