We have developed and validated a selective analytical procedure, based on ion-exchange normal-phase liquid chromatography with fluorescence detection and liquid-liquid extraction, for the analysis of vinblastine (VBL) in biological matrices. The assay is suitable for the determination of the parent compound and its metabolites in plasma, tissue, faeces and urine specimens. Pharmacokinetics studies were performed in male FVB mice receiving VBL by intravenous (i.v.) bolus injection at a dose of 6 mg/kg. Plasma concentrations were monitored until 48 h after drug administration. Urine and faeces samples were collected in 24-h portions for up to 72 h and tissue samples were obtained at 4, 24, 72 and 168 h after drug administration. To facilitate a comparison between the findings we obtained by high-performance liquid chromatography (HPLC) and the results of previous studies using radiolabeled drug monitoring, some of the animals were also given radiolabeled drug. Large discrepancies were observed between the results obtained by the two methods. Excretion of the radiolabel in faeces and urine was 85% of the dose within 72 h. HPLC revealed that only 18% of the dose was excreted as unchanged drug and 19%, as measurable metabolites [O4-deacetylvinblastine (DVBL) and two unknown compounds]. In most of the tissues taken at 4 h after drug administration, virtually all of the radioactivity represented VBL or DVBL. In all tissues taken at 72 h after drug administration, however, only very little of the radioactivity remained in the form of these compounds. Following the administration, VBL and DVBL were distributed extensively to most tissues. Many tissues appeared to possess effective means of extruding the cytotoxic drug with decreasing plasma levels. However, in some organs, including those from the genital tract and lymphatic tissues, VBL and DVBL were retained for prolonged periods. Our studies confirm previous indications that selective retention may be the basis of the activity of VBL against malignant transformations derived from these tissues.