The high pressure liquid chromatography (HPLC) was used for the quantitative determination of R- and S-epimers of latamoxef, cefotaxime and desacetylcefotaxime in serum and bile. Bile levels of latamoxef, 1 and 2 h following administration of the antibiotic, were markedly above serum values. Those of cefotaxime, however, were identical after 1 h, after 2 h bile levels were below serum values. Desacetylcefotaxime concentration in bile after 1 and 2 h was four to five times higher than in serum. The ratio R-:S-epimer of latamoxef in serum was 49:51 after 1 and 2 h, in bile 44:56 after 1 h and 48:52 after 2 h. In the case of latamoxef the comparison of the microbiological and the HPLC assay showed good correlation (r = 0.98). The ratio cefotaxime: desacetylcefotaxime in serum was 72.5:27.5 after 1 h and 61.5:38.5 after 2 h, in bile 41:59 after 1 h and 24:76 after 2 h.