Haematopoietic tissues are the targets of numerous xenobiotics. The purpose of in vitro haematotoxicology is the prediction of adverse haematological effects from toxicants on human haematopoietic targets under controlled experimental conditions in the laboratory. Building on its foundations in experimental haematology and the wealth of haematotoxicological data found in experimental oncology, this field of alternative toxicology has developed rapidly during the past decade. Preclinical and clinical drug development for anti-cancer drugs differs from that for other pharmaceuticals, because of the life-threatening nature of the disease. Treatment with anti-cancer drugs at clinically efficacious doses usually induces serious side-effects. The design of preclinical toxicology studies for anti-cancer drugs is intended to identify a safe clinical starting dose, characterise toxicities that could be encountered in human clinical trials, and determine whether these toxicities are reversible, manageable, and predictable. Although the myeloid colony-forming unit (CFU-GM) progenitor is most frequently evaluated, other defined progenitors and stem cells, as well as cell types found in the marrow stroma, can now be evaluated in vitro. Genetic damage to haematopoietic cells can occur in the absence of any overt haematological signs. The development of tissue-specific screening systems that are able to give information about the toxic effects of chemicals, drugs and environmental hazards on target genes is needed, in order to make preliminary decisions or to set priorities for selection among large groups of chemicals and possible drugs.