Ketorolac tromethamine, a new nonsteroidal antiinflammatory analgesic, was evaluated for relative efficacy, safety and time course of analgesia in a stratified, randomized, parallel, double-blind trial. The study involved 120 hospitalized women (4 groups of 30) with moderate or severe postpartum uterine pain treated with single oral doses of ketorolac 5 mg and 10 mg, aspirin 650 mg or placebo. At regular interviews for 6 hours patients rated pain intensity, pain relief and side effects. Significant differences (p less than or equal to 0.05, two-tailed) occurred among the 4 treatments for various measurements of summed and peak analgesia. Ketorolac 10 mg was significantly superior to placebo in 5 of 5 major efficacy measurements, and aspirin was significantly superior in 3 of 5. Ketorolac 10 mg gave the highest mean rating for summed pain intensity differences (13.6, p = 0.0002 versus placebo), followed by aspirin (11.9, p = 0.012), ketorolac 5 mg (10.9, p = 0.072) and placebo (8.6). With ketorolac 10 mg and 5 mg and aspirin, analgesia lasted 6 hours, with peak efficacy at 3 hours. Side effects were not significant. Our results suggested a positive dose-response relationship for ketorolac. Compared to aspirin, ketorolac 10 mg induced equal or more analgesia, whereas ketorolac 5 mg was near the minimum effective dose and seemed less effective than aspirin.