This double-blind, randomized, parallel, placebo-controlled study evaluated the analgesic effects of single oral doses of 30 mg nalbuphine, 650 mg acetaminophen, and the contribution of each to the efficacy of their combination in 128 hospitalized patients with postoperative pain. Subjective reports of patients evaluated each hour for 6 hours were used as indices of analgesic response. Both nalbuphine and acetaminophen were significantly superior to placebo for most measures of total and peak analgesia. The interaction contrast between nalbuphine and acetaminophen was not significant for any analgesic measurements, indicating an additive effect of the components. The combination was the most effective treatment, followed by nalbuphine, acetaminophen, and placebo. Effects of the combination were significantly different from those of acetaminophen at 4, 5, and 6 hours and from those of placebo at 1 to 6 hours. There was no significant difference in the frequency or intensity of side effects among the groups. The combination of nalbuphine and acetaminophen appears to be a therapeutically useful combination.