A number of studies have suggested that nonsteroidal antiinflammatory agents can relieve renal colic by a mechanism of action different from that of narcotics, offering the potential advantage of avoiding narcotic side-effects such as alteration of mental status. The authors prospectively administered oral indomethacin, 50 mg, to 25 nonvomiting patients with acute renal colic due to a documented stone. Eleven patients group (I) received the drug in an unblinded, nonrandomized fashion after failure of oral or parenteral narcotics to provide satisfactory pain relief, either at home or in the emergency department. In 14 additional patients group (II) indomethacin was given as the only initial treatment. Pain intensity before and after treatment was reported using a 1-to-10 scale. In group I, pain decreased from 5.8 +/- 2.7 to 3.6 +/- 3.8 (P less than .02). Six of the 11 patients reported a decrease in pain intensity of 50% or more, which occurred within 25 +/- 11 minutes, and in 5 of these 6, pain decreased to a 0 or 1 level. In group II, pain decreased from 7.6 +/- 1.5 to 4.6 +/- 4.0 (P less than .008). Eight of the 14 patients reported a decrease in pain intensity of 50% or more, which occurred within 40 +/- 14 minutes, and in 5 of these 8 pain decreased to a 0 or 1 level. Among all 25 patients who received indomethacin, pain relief was not significantly associated with the duration of pain before treatment or with patient age or sex. There was a trend for pretreatment pain intensity to be higher among nonresponders (P = .07).(ABSTRACT TRUNCATED AT 250 WORDS)