The major side effect of anticancer drugs is damage to the hematopoietic system. These compounds may interfere with cell proliferation and differentiation in different blood lineages causing many diseases such as neutropenia, aplastic anaemia or trombocytopenia. The clonogenic assays are useful in vitro tools for evaluating and predicting acute xenobiotics myelotoxicity. A miniaturisation of these assays, in order to reduce costs and increase the number of compounds that could be tested, is under investigation. The in vitro sensitivity of human burst-forming unit erythroid (BFU-E) and colony-forming unit granulocyte-macrophage (CFU-GM) to three anticancer drugs: cyclophosphamide (CTX), 5-fluorouracil (5-FU) and taxol (TAX) was evaluated both in 35 mm plate and 96-well plate systems and the dose-response curves, IC50 values and IC90 values were compared. The correlation between in vitro data and clinical plasma levels confirms that severe hematotoxicity is the primary adverse effect of these drugs with an evident selectivity on erythroid progenitors for cyclophosphamide. IC50 and IC90 values, calculated on the basis of results obtained with the traditional assay, correlate with those obtained in microplate, as well as the dose-response curves, indicating that the 96 well plate assay could be a useful and reliable tool for high-throughput screening in early stages of drug development.