The pharmacokinetics of esorubicin, a new anthracycline antibiotic, was investigated in conjunction with a phase I clinical trial. The drug was administered to 12 patients as an intravenous bolus at a dose of 20 to 40 mg/m2. All patients had normal renal and hepatic functions and no third space fluid accumulation. Plasma and urine samples were assayed by HPLC. The peak plasma concentration of esorubicin was 0.74 +/- 0.57 microM (mean +/- SE). Esorubicin disappeared from plasma according to a tri-exponential pattern with a terminal half-life of 20.4 +/- 7.3 hr. The area under the plasma concentration versus time curve was 0.64 +/- 0.31 microM x hr. Total body plasma clearance was 45.5 +/- 26.8 liter/min/m2 and the apparent volume of the central compartment, 41.0 +/- 24.8 L. A single metabolite, 4'-deoxydoxorubicinol, was detected in plasma. This metabolite was observed in 5 patients only and its mean peak concentration was 0.029 +/- 0.017 microM. The area under the plasma versus concentration time curve for 4'-deoxydoxorubicinol was 0.02 +/- 0.014 microM xhr. The urinary excretion of total fluorescence within 5 days of therapy was 7.3 +/- 1.3% of the administered dose. Esorubicin represented more than 80% of the excreted anthracyclines. As in plasma, 4'-deoxydoxorubicinol was the only metabolite detectable in urine. No correlation between the various pharmacokinetic parameters and drug-induced toxicity was observed in this small group of patients.