We examined the effect of 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) and a variety of vitamin D analogs on proliferation and differentiation of normal and leukemic myeloid clonogenic cells. Only cells from myeloid leukemic lines that contained relatively mature cells (HL-60, U937, THP, HEL, M1) were induced to differentiate and were inhibited in their clonal growth by exposure to 1 alpha,25(OH)2D3 (50% inhibition, 3 X 10(-8)-8 X 10(-10) M). A fluorinated analog of vitamin D was 5-10-fold more potent than 1 alpha,25(OH)2D3. Cells from a human myeloblast line (KG-1) and normal human granulocyte-monocyte stem cells (GM-CFC), both of which depend on colony-stimulating factor (CSF) for clonal growth, were stimulated in their clonal proliferation by 1 alpha,25(OH)2D3 in the presence of suboptimal concentrations of CSF. Leukemic cells from 10 of 14 patients with myeloid leukemia, but not normal GM-CFC from 12 patients in remission, were markedly inhibited in their clonal proliferation by 1 alpha,25(OH)2D3. Our results suggest that 1 alpha,25(OH)2D3 may be a cofactor in hematopoiesis and that vitamin D analogs may have a differential effect on normal versus leukemic growth.