In a double-blind, single-dose, parallel-group study, ketorolac (5, 10, or 20 mg) was compared with acetaminophen (500 or 1000 mg) when taken by mouth for postoperative orthopedic pain. Analgesic measurements were made by trained nurse observers who used standard verbal rating and visual analog scales. Acetaminophen, 1000 mg, was statistically superior to 500 mg acetaminophen, demonstrating assay sensitivity. Ketorolac, 20 mg, was distinguished from 500 mg acetaminophen, 5 mg ketorolac, and 10 mg ketorolac, but not from 1000 mg acetaminophen. The higher doses of ketorolac induced a longer lasting peak analgesic effect than did acetaminophen, but the magnitude of the peak pain relief was changed little by an increased ketorolac dose. Overall, 10 mg ketorolac appeared equivalent to 1000 mg acetaminophen. Acetaminophen, 500 mg, induced less sedation than the higher doses of ketorolac, but neither drug caused untoward side effects.