Progenitor cells of bovine erythrocytes, megakaryocytes, and granulocyte-macrophages were cultured in agar or methylcellulose media. Colony formation was supported by cell-free conditioned medium from short-term cultures of concanavalin A-stimulated bovine peripheral blood leukocytes. Granulocyte-macrophage progenitors proliferated well in both types of semisolid culture media, giving rise to neutrophils (from granulocyte colony-forming units, CFU-G), eosinophils (from eosinophil CFU, CFU-Eo), monocyte-macrophages (from macrophage CFU, CFU-M), and mixed granulocyte-macrophages (from granulocyte-macrophage CFU, CFU-GM). Better growth of megakaryocytes, as well as late (erythroid CFU, CFU-E) and early (erythroid burst-forming units, BFU-E) erythroid progenitors was obtained with methylcellulose. Despite considerable variation in the numbers and types of colonies formed from different aspirates of bovine marrow, the numbers observed were generally comparable to those obtained from human and mouse bone marrow cells. The proliferation of bovine BFU-E and eosinophil progenitors herein described is the first successful report of the culture of these cell types.