In a double-blind study, 198 outpatients with pain after oral surgery were randomly assigned to treatment with a single oral dose of naproxen sodium 550 mg, codeine sulfate 60 mg, a combination of naproxen sodium 550 mg with codeine sulfate 60 mg, aspirin 650 mg or placebo. Using a self-rating record, subjects rated their pain and its relief hourly for 12 hours after medication. Orthogonal contrasts for the four treatments making up the factorial component showed that the naproxen effect was significant for every measurement of total and peak analgesia; the codeine effect was significant for total and peak pain relief and patients' overall evaluation. The naproxen-codeine interaction was not statistically significant for any measure, which suggests that the analgesic effect of the combination represents the additive effect of its constituents. Based on pairwise comparisons, aspirin was significantly superior to placebo for most measures of effect, naproxen was significantly superior to both aspirin and codeine for all measures and the combination was significantly superior to naproxen for patients' overall evaluation. No more patients experienced adverse effects with aspirin or naproxen than with placebo, but significantly more patients receiving the codeine-containing treatments experienced adverse effects than those receiving aspirin and naproxen.