The purpose of our investigation was to evaluate the pharmacokinetic profile of doxorubicin administered by a new schedule. Nine non-pretreated young women with high risk breast cancer (mean age: 38, range: 29-45) entered this trial and received, cyclophosphamide (600 mg/m2) given as a 30-min infusion followed by doxorubicin (120 mg/m2) as a continuous infusion over 6 h. Chemotherapy was combined with hematopoietic factor support (G-CSF or GM-CSF). Blood was sampled over the 0-54 h period and 14 cycles were studied for pharmacokinetics. Doxorubicin as well as its major metabolite doxorubicinol were assayed in plasma specimen by high performance liquid chromatography. Mean doxorubicin plasma concentration peak was 42.6 ng/ml (standard deviation (SD): 13.3). The mean terminal half-lives were 32.6 h (SD: 22.0) and 39.2 h (SD: 21.6) for doxorubicin and doxorubicinol, respectively. Mean areas under the plasma concentration-time curve (AUC) were 413 ng/h-1 ml (SD: 103) and 1,707 ng/h-1 ml (SD: 815) for doxorubicin and doxorubicinol respectively. Consequently, the ratio of the AUC of doxorubicinol to that of doxorubicin was high (mean: 4.1 (SD: 1.6)) contrasting with previous studies reporting ratios less than 1 in patients with normal liver function. The systemic clearance of doxorubicin was 5.23 l/min/m2 (SD: 1.91). The inter- and intra-patient variability for AUC was low for both drugs. Hence the coefficients of variation were 24.6% for doxorubicin, 26.2% for doxorubicinol (inter-individual variation) and less than 10% for both compounds (intra-individual variation). In conclusion, the pharmacokinetic profile of doxorubicin (120 mg/m2) administered as a 6 h-continuous infusion is characterized by a greater exposure to doxorubicinol. This could be explained by a saturation in the biliary excretion process during the period following the end of the infusion.