To study the role of prostaglandin production by detrusor muscle in women with idiopathic primary detrusor instability, biopsies of detrusor muscle were obtained from 20 women. Nine women had detrusor instability, and 11 women had stable bladders. Prostaglandin F2 alpha and the stable metabolites of prostacyclin and thromboxane A2, namely, 6-keto-prostaglandin F1 alpha and thromboxane B2, respectively, were measured after in vitro incubations of detrusor muscle for 3 hours. A significant reduction in the production of 6-keto-prostaglandin1 alpha in women with detrusor instability was noted. There were no differences in the production of prostaglandin F2 alpha and thromboxane B2, between women with stable and unstable bladders. These results suggest for the first time that women with idiopathic primary detrusor instability may have a deficient production of prostacyclin.