An in vitro study was carried out to evaluate the possible protective effect of recombinant human erythropoietin (rhEpo) on cisplatin (CDDP)-induced inhibition of erythroid colony growth. CDDP at the dose of 0.4 mg/ml caused a 72-75% inhibition of erythroid stem cell growth in plasma clots. In the short-term assay rhEpo was not able to protect normal murine erythroid stem cells from the inhibitory effect of CDDP at any of the tested concentrations. In long-term bone marrow cultures, although the kinetics of cellular populations in suspensions and of erythroid stem cells were similar in both controls and CDDP-treated cultures, both cellularity and erythroid stem cells levels were much lower in CDDP-treated flasks than in control ones regardless of the addition of rhEpo. These results indicate that rhEpo is not able to prevent of ameliorate erythroid stem cell inhibition due to a possible toxic effect of CDDP, at least in vitro.