To determine the effects of indomethacin suppositories in the relief of acute colic and prevention of recurrent colic, we instituted a prospective double-blind, placebo-controlled protocol. Patients were randomized to receive either 50 mg. indomethacin or placebo suppositories every 8 hours and all patients received prescriptions for supplemental narcotics to be used on an as needed basis. Relief of colic was assessed by counting the total number of supplemental narcotics used by each patient per 24 hours during the study period, which was defined as until passage of the calculus or 5 days. There were 41 patients entered into the study protocol and complete follow-up was available for 26. Mean calculus size was 3.4 mm. in the indomethacin group versus 3.1 mm. in the placebo group. All 13 patients in the control group had recurrent episodes of colic and 8 of these 13 had more than 1 recurrent episodes. Five patients in the placebo group required admission to the hospital for control of pain. In contrast, only 4 of the 13 patients in the treatment group had colic and only 1 had more than 1 episode of colic. No patients in the active drug group required admission to the hospital for control of pain. Over-all the ratio of supplemental narcotic used by the placebo group versus the indomethacin group was 7.6:1 (p < 0.005). The mean interval time to passage of the calculus was slightly lower in the indomethacin group (89 versus 82 hours) but this difference was not statistically significant (p > 0.10). Our data strongly support the use of the indomethacin suppositories in the prevention of recurrent colic secondary to ureteral calculi.