Flupenthixol (FP), nortriptyline (NT) and zuclopenthixol, (ZCP) were determined in breast milk and plasma from 2 puerperal, lactating women with psychiatric disorders. The milk concentrations were equal to, higher and lower than those in plasma for FP, NT and ZCP, respectively. Variation in milk triglyceride concentration, but not milk pH, could partly explain between-breast differences in the milk concentrations. The study demonstrates the need for appropriate and representative milk sampling procedures. The estimated daily infant exposure averaged 0.5, 2.3 and 0.3% of the corresponding maternal weight related doses of FP, NT and ZCP. FP was also detectable in infant plasma. These drugs are not known to be harmful in small doses to breast-fed infants. However, concern about the effect of dopamine blocking agents on neurobehavioral mechanisms in animals warrants caution. If neuroleptics are required for a long period this risk must be weighed against the benefits of breast-feeding, also considering the psychological effects of the latter.