The human cell line U 937 spontaneously expresses monocytic maturation and can be induced into macrophage-like cells when treated with retinoic acid, sodium butyrate, or 2,3-O-tetra decanoylphorbol-13-acetate. We have selected a subclone, designated UM 384, that expresses granulocytic characteristics and can be induced to mature to granulocytes after exposure to retinoic acid, actinomycin D, and dimethylsulfoxide, and to monocyte-like cells when treated with sodium butyrate and phytohemagglutinin-stimulated leukocyte-conditioned medium. These cells retain the same constitutive markers as the parent line including histocompatibility leukocyte antigens and karyotype but share numerous chromosomal abnormalities, mainly t(X;8) (p21;q12).