Simultaneous blood and milk samples were obtained from a 30-year-old woman who was on sustained release amitriptyline, and the concentrations of amitriptyline and the active metabolite, nortriptyline, were estimated by GLC. Serum and milk concentrations were similar with a slight tendency for the amitriptyline concentrations to be higher in milk. Calculation of the transfer of drug from the mother to the baby showed that the baby received an amitriptyline dose which was about one hundredth the dose given to the mother. No active drug could be estimated in the baby's serum and the baby showed no clinical signs which could be drug related.