The phagocytizing and colony-stimulating activities of liver macrophages are increased 36 h after partial hepatectomy. Although the blood count of phagocytizing cells is increased, the rate of the formation of zymosan-induced granulomas in the liver and lungs is decreased. Administration of zymosan after partial hepatectomy inhibits granulomonocytopoiesis in the bone marrow and reduces colony-stimulating activity of Kupffer cells and phagocytizing activity of liver and lung macrophages.