Sufentanil 3 microgram kg-1 was administered as an intravenous (i.v.) bolus to 12 elderly patients, aged 65-87 years and 12 young adults, 17-43 years of age, all ASA class I-II, scheduled for orthopaedic surgery. Plasma sufentanil concentrations were measured by a specific radioimmunoassay. Plasma concentration time-curves for the young adult and the elderly groups were superimposible. Pharmacokinetic parameters were calculated from the derived compartmental models. Elimination half-lives, clearance and total volumes of distribution were calculated with non-compartment methods. The major pharmacokinetic parameters, elimination half-life, clearance and volume of distribution did not differ between both groups. The age-related differences in the action of sufentanil cannot be explained by its pharmacokinetic properties.