Angelmicin B is a new microbial substance which inhibits src tyrosine kinase activity and oncogenic signal transduction. We investigated the effect of angelmicin B on the proliferation and differentiation of the HL-60 human myeloid leukemia cell line. Angelmicin B caused the dose-dependent inhibition of cell proliferation and induction of differentiation along the myelomonocytic pathway, as determined by morphological changes, nitroblue tetrazolium (NBT) reduction, and non-specific esterase and lysozyme activities at concentrations ranging from 0.1 to 0.5 microgram/ml. Also, it induced significantly the differentiation of mouse myeloid leukemia M1 cells. A similar concentration of angelmicin B inhibited the growth of the myeloid leukemia cell lines K562, HEL, KU812, ML-1, U937 and THP-1, but did not induce differentiation of these cells significantly. The differentiation of HL-60 cells was enhanced by combined treatment with angelmicin B and 1 alpha, 25-dihydroxyvitamin D3 (VD3), retinoic acid or tumor necrosis factor-alpha (TNF alpha). Angelmicin analogs (A1, A2, B, C and D) had almost equivalent effects on the differentiation of HL-60 cells, although angelmicins C and D inhibited src tyrosine kinase activity less than the other analogs. The effective concentrations of angelmicin B in src kinase inactivation was about 100-fold higher than those required for the growth inhibition and differentiation induction. These findings indicate that the differentiation-inducing activity of angelmicins is not associated with their src kinase-inhibiting activity, and may be associated with the modulation of other signal pathway(s).