A single oral dose of 75mg nortriptyline was given to a group of 20 depressed elderly patients in hospital. Subsequent plasma nortriptyline concentrations were used to calculate the half-life and clearance of the drug. These measurements were compared with those made previously in 17 healthy young volunteer subjects.Plasma nortriptyline half-life was longer and clearance slower (p < 0.002) in the elderly group than in the volunteers. There was no correlation of age with either of these parameters within the 2 groups, and no differences in nortriptyline pharmacokinetics could be detected between the male and female volunteer subjects. The possible reasons for these findings and their clinical consequences are discussed.