Plasma and milk concentrations of doxorubicin (DOX) and cisplatin were measured after iv administration of these agents to a lactating patient with ovarian cancer. Cisplatin was undetectable in human milk. Milk concentrations of DOX often exceeded those detected in concomitant plasma samples. For DOX, the highest milk:plasma concentration ratio was 4.43:1 and was observed 24 hours after administration of the drug. The area under concentration versus time curve (AUC) for DOX was approximately the same in plasma and milk. Doxorubicinol was the major metabolite of DOX in plasma and in milk. The AUC for doxorubicinol was ten times higher in milk than in plasma. However, the total amount of anthracycline antibiotic delivered in the milk (maximum concentration of active anthracycline antibiotic: 0.24 mg/L) was negligible.