Twenty-eight healthy volunteers (age range, 22-78 years) received 650 mg of acetaminophen (AAP) on three separate occasions. The modes of administration were 1) intravenous, 5-minute infusion; 2) oral, with two 325-mg tablets; and 3) oral, with 650 mg as an elixir preparation. Plasma levels of AAP were determined in blood samples drawn up to 12 hours after the dose. The mean (+/- sd) kinetic variables for absorption of AAP from tablets in young and elderly were peak plasma concentration, 11.8 (+/- 4.2) vs 10.9 (+/- 4.1) micrograms/ml; peak time, 0.79 (+/- .54) vs 0.69 (+/- .40) hours after the dose; absorption half-life, 12.6 (+/- 9.8) vs. 8.2 (+/- 5.3) minutes; and absolute systemic availability, 79 (+/- 9) vs 72 (+/- 11) per cent. For AAP elixir, the corresponding values were 12.6 (+/- 5.4) vs 13.7 (+/- 6.0) micrograms/ml; 0.52 (+/- .24) vs 0.54 (+/- .51) hours; 8.6 (+/- 6.2) vs 6.1 (+/- 6.6) minutes; and 87 (+/- 9) vs 80 (+/- 9) per cent. Absolute bioavailability of both oral dosage forms was significantly less then 100 per cent in all groups. Elderly subjects tended to show lower availability of both oral preparations, but the difference was of borderline significance (P less than .50). Age did not influence any other measures of absorption. Since the absorption rate of acetaminophen may be indicative of the gastric emptying rate, age does not appear to alter this rate-limiting step in drug absorption.