A single-dose, double-blind, randomized, parallel trial was conducted to compare the analgesic efficacy of oral ibuprofen (I) 100, 200, or 400 mg, aspirin (ASA) 650 mg, and placebo in moderate to severe pain after extraction of impacted teeth. Subjective, self-evaluated pain intensity and pain relief reports, hourly for 6 hours, were used as indexes of analgesic response. Data on 227 evaluable patients showed significant differences among the 4 active treatments and placebo (p less than 0.001) by most measurements of analgesia. Although no consistent, significant differences were observed among the active drugs, I 400 mg performed the best, followed by I 200 mg, ASA 650 mg, and I 100 mg. Remedication was required by 59% patients receiving I 400 mg, 67% taking I 200 mg, 73% taking ASA 650 mg, 74% taking I 100 mg, and 96% receiving placebo. Differences between I 400 mg and I 100 mg were significant for remedication data (p less than 0.05). Side effects were minor, infrequent, and not dose related. In this study, I 100 mg was distinctly superior to placebo and probably as effective as ASA 650 mg in relieving pain. Only a shallow dose response of ibuprofen was observed.