The sequence dependency of the interaction of taxol with other anticancer drugs is of clinical importance, and may be due to pharmacokinetic changes and/or to inherent differences in the sensitivity of target normal or cancer cells. This study presents results on the in vitro interaction of taxol with doxorubicin, cisplatin, etoposide and vinorelbine in alternate sequences on human hemopoietic progenitors (CFU-GM). Peripheral blood mononuclear non adherent cells were exposed to IC50 of Taxol for 24 hours and then, for 1 hour to IC50 of each of the other drugs. In a second set of experiments the reverse sequence was applied. The cell suspension was subsequently cultured to assay the growth of CFU-GM. A strong sequence dependency characterizes the combination taxol-vinorelbine, while for the other combinations the order of sequence appears to have little impact on in vitro toxicity on CFU-GM. Comparing results on CFU-GM with that obtained in vitro with the same combination sequences on cancer cell lines some remarkable differences show up. Studies on a normal human myeloid line may therefore have a place in preclinical evaluation of sequence of anticancer drug combinations.