Upon incubation with paclitaxel, B16-F1 melanoma cells showed a flattening and darkening of their cytoplasm. By electron microscopy analysis, an increase in the number of melanosomes associated with an increase of their melanin content was observed. The cells also showed prominent morphological changes such as flattening, loss of prolongation and increase in size. Tyrosinase activity was increased 2.2 fold after 16 hours of incubation with 10 microM paclitaxel. The tyrosinase gene transcription was evaluated by semi-quantitative RT-PCR. The mRNA level was not significantly increased indicating that the effect of paclitaxel on melanogenesis was probably due to post-transcriptional events.