Lipoxins A4 and B4 together with the all-trans lipoxin (LX) isomers were produced by normal human bone marrow cell suspensions after incubation with ionophore A23187. Both LXA4 and LXB4 enhanced the growth of myeloid progenitor cells in semisolid agar in the presence of suboptimal concentrations of recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF). Lipoxin A4 at 10(-10) M stimulated the colony formation in 13 out of 15 tested human bone marrows with a mean (+/- SEM) increase of 47 +/- 11% (p = 0.001). A similar stimulatory effect was observed after addition of LXB4 (10(-10) M). The monohydroxyeicosatetraenoic acids 5-, 12- and 15-HETE did not affect colony growth. In addition, LXA4 (10(-8) M) efficiently counteracted the increased colony formation induced by leukotriene C4 (10(-10) M), suggesting an antagonistic relationship between these lipoxygenase products. The results support a role for lipoxins in the regulation of human myelopoiesis.