The etiology of drug-induced agranulocytosis is poorly understood. Many drugs that induce neutropenia or agranulocytosis can be metabolized to reactive intermediates that covalently bind to macromolecules. Until now, the myeloid precursor cell or an earlier committed progenitor cell has been favoured as the target for toxicity, due to evidence in some cases of cytotoxic action or antibodies against neutrophils. In the bone marrow, where neutrophils mature, certain components of the stromal microenvironment, e.g. intracellular adhesion molecule 1, vascular cell adhesion molecule 1, CD11b/CD18, heparan sulfate proteoglycans, fibronectin and hemonectin are essential for normal myeloid maturation. This article proposes that drugs implicated in agranulocytosis, or more likely their reactive metabolites, interact with specific components of the extracellular matrix and interfere with the normal regulation of granulopoiesis.