4'-Epidoxorubicin, doxorubicin (internal standard) and eight metabolites were extracted from heart tissue homogenate by a mixture of tetrahydrofuran-water (1:2, v/v) and purified by C18 Sep-Pak cartridges. The buffer used to prepare the homogenate contained glucaric acid-1,4-lactone and glucose, to prevent decomposition of the 4'-epidoxorubicin glucuronides. Anthracyclines were separated by high-performance liquid chromatography within 14 min and detected by fluorescence. Recoveries ranged from 49 to 75%. The detection limits of the individual anthracyclines ranged from 0.5.10(-11) to 2.5.10(-11) mol/g wet weight. The peak-height ratios of the fluorescence intensities of the anthracyclines versus doxorubicin were linear from 2.5.10(-11) to 250.10(-11) mol/g wet weight. Within- and between-day precisions of the assay varied between the anthracyclines and were in the ranges 3-12% (n = 6) and 2-11% (n = 6), respectively.