Patients with the irritable bowel syndrome were studied with regard to the effects of beta-adrenoceptor agonists on rectosigmoid motility. Pressure was recorded with a continuously inflated balloon in the upper rectum and recorded from a pressure catheter in the sigmoid colon. On different days the beta-2 agonist terbutaline, the beta-1 agonist prenalterol, and placebo, respectively, were administered intravenously after a control period. During each examination contractile activity was quantified for three consecutive periods of 25 min. Terbutaline in a total dose of 0.50 mg decreased sigmoid motility index significantly from 3.0 +/- 0.6 (SEM) to 1.1 +/- 0.3 kPa X min (p less than 0.01). After less than or equal to 5 mg prenalterol no significant changes of motility index were observed. After placebo an increase, although not significant, in contractile activity was seen compared with the initial control period. Rectal motility indices were low and not changed by the beta agonists. The serum concentrations of the drugs were within the therapeutic limits used in clinical practice and caused a dose-dependent increase of both systolic blood pressure and heart rate. It is concluded that beta-2 adrenoceptor stimulation significantly decreases sigmoid motility whereas the motility index seems to be unaffected by beta-1 adrenergic stimulation.