A human eosinophilic leukemia cell line, designated as EoL, was established from the peripheral blood of a patient with Philadelphia chromosome-negative eosinophilic leukemia (EL). The EoL cell line grows in single cell suspension with a doubling time of 48 hours for about one year. The reactivity of these cells was tested with a panel of monoclonal antibodies; they were found to express surface IA antigen, myeloid antigen (IF10, MY9) and membrane receptors for interleukin 2 (IL-2, Tac antigen). Under standard culture conditions, a small percentage of cells having more typical eosinophilic characteristics was present. These cells had cytoplasmic granules and were positive for Luxol-fast-blue and eosinophil peroxidase. Under culture conditions to induce the maturation of myeloid cells, such as alkaline medium or addition of dimethyl sulfoxide (DMSO), the frequency of cells with typical eosinophilic features increased to about 40%. In addition, cytogenetic studies showed that cultured cells and original leukemic blasts presented similar chromosome abnormalities. EoL seems to be a unique leukemic line committed to the eosinophilic lineage and can provide a useful in vitro model for the study of malignant eosinophilic properties.