A simple method was developed for the routine monitoring of daunorubicin (DR) or adriamycin (ADR) and of their chief fluorescent metabolites in plasma of cancer patients. The plasma samples were treated with ethanol: hydrochloric acid mixture, following which the drug and its metabolites, released to the 40,000 g supernatant, were analyzed by HPLC. A mu-bondapak-phenyl column was used and an isocratic mobile phase consisting of acetonitrile in 0.1 M ammonium-formate buffer at pH 4.0. Average recovery of all the tested compounds within the concentration range of 17-3,450 pmol/ml plasma was 108 +/- 5% (mean +/- SD). The method was applied to analyses of plasma samples of several patients treated with DR or ADR. At 3 h after treatment with a DR dose of 45 mg/m2 or 60 mg/m2, daunorubicinol was the major metabolite and its concentrations were 46-270 or 85-305 pmol/ml, respectively; the unchanged drug was present at concentrations of 16-99 or 30-101 pmol/ml, respectively. Deoxydaunorubicinolone and deoxydaunorubicinone were detected at concentrations ranging from 0 to 89 pmoles/ml in the plasma of some patients. Plasma of patients treated with ADR (30 mg/m2) contained adriamycinol as the main detectable metabolite, but at 3 h after treatment its concentration was usually lower than that of the unchanged drug (22 +/- 9 vs 53 +/- 16 pmol/ml). Traces of 7-deoxyaglycones were detected in some plasma samples.