Age, gender and female sex hormones are thought to influence contractility of the gallbladder. Surgically removed gallbladders with gallstones and mild chronic cholecystitis from three groups of patients (males and premenopausal and postmenopausal females) were studied. Strips were incubated in Krebs solution, in Krebs containing 0.2 per cent ethanol-propylene glycol solvent (solvent controls) or in Krebs solution containing progesterone (0.1, 1.0 and 10.0 micromolar) or 17-beta-estradiol (0.1 and 1.0 micromolar). Concentration response curves were obtained for acetylcholine and octapeptide of cholecystokinin and the maximum contraction and median effective dose values were recorded. Steroid receptor levels in the wall of the gallbladder were also estimated. In gallbladders from males, the sensitivity to acetylcholine increased significantly with age. However, in gallbladders from premenopausal women, there was a significant decrease in sensitivity to acetylcholine and cholecystokinin with age. Progesterone (1 and 10 micromolar) reduced the spontaneous rhythmic contractions of the strips by 35 +/- 8 and 65 +/- 8 per cent, respectively, and also reduced the maximum contraction of gallbladders from postmenopausal females to acetylcholine. Estradiol-17 beta had no effect upon the contractility of the gallbladder. The results of additional studies showed that the human gallbladder is estrogen and progesterone receptor negative. The sensitivity of the gallbladder to neurohormonal stimulation varies with age and gender. These results indicate that short term exposure to female sex hormones has an inhibitory effect upon gallbladder contractility. The inhibitory effects of short term exposure to progesterone seen in this study are probably nonspecific in nature.