It is well established that basophils and eosinophils share a common differentiation pathway, although the factors regulating their terminal commitment (towards one or other lineage) are not yet fully defined. Interleukin-3 (IL-3) is a major differentiation factor for both human eosinophils and basophils, yielding a mixed population composed predominantly of eosinophilic cells (65 ± 9%; n = 4), basophils at different stages of maturity (29 ± 6%; n = 4) and monocytes/macrophages (6 ± 3%; n = 4), after 3–4 weeks in culture. Using a relatively rapid and simple method involving a first step of gradient density centrifugation over a Percoll gradient (d = 1.063 g/ml) and a subsequent step of adhesion on tissue-culture-treated plastic, a cell population composed of 94 ± 5% normal basophils and their precursors, with no demonstrable mast cells, was reproducibly obtained from human hematopoietic cells cultured for 3-A weeks in the presence of recombinant IL-3. These cells contained high levels of histamine (1.39 ± 0.14 pg/cell) and released this mediator upon stimulation with calcium ionophore A23187 and in a dose dependent manner upon stimulation with IgE-anti IgE, demonstrating their functional capacity. This relatively simple method therefore permits the production of large quantities of pure populations of normal and functional human bone-marrow-derived-basophils.