The pharmacokinetic parameters of nortriptyline in the pediatric age group following oral administration of a single dose of 25 or 50 mg were investigated from nortriptyline plasma level assays at 12, 18, 24, 36, and 48 hours postdose. Data were analyzed separately for the nine prepubertal and 11 postpubertal subjects, all of whom were diagnosed major depressive disorder. These data were compared with studies in the literature of nortriptyline pharmacokinetics from adult and geriatric normal and depressed populations. Similar to adults, the elimination of nortriptyline in children and adolescents is apparently first order kinetics with a logarithmically linear rate of disappearance. The prepubertals had a shorter mean half-life (17.6 +/- 3.7 hours) than some adult groups and twice a day dosage would, therefore, be more appropriate for many children. Although the mean half-life (27.1 +/- 17.1 hours) for the adolescent group suggested that once a day dosage would be sufficient, some adolescents would need twice a day dosage for optimum plasma level control because there was a wide range (14.1 to 76.2 hours). The almost twofold variation in half-life in prepubertals and fivefold variation in postpubertals were similar to differences in adult groups and emphasize the value of plasma level monitoring in the clinical use of nortriptyline.