Purified populations of monocyte, T lymphocyte, and B lymphocyte from normal human peripheral blood were used for the investigation of elaboration/release of granulocyte-macrophage colony-stimulating activity (GM-CSA). Cell separation was performed by a series of techniques including density-cut centrifugation, adhering incubation, carbonyl iron ingestion and E rosette formation. The purity of the isolated cell population was over 95% with a mean viability of 98%. After collection, the cells were resuspended at a concentration of 1 x 10(6)/ml in RPMI-1640 medium containing 5% fetal calf serum and incubated for 7 days at 37 degrees C to prepare conditioned media (CM) for assay of GM-CSA. The results showed that the monocytes could constitutively secrete a considerable amount of GM-CSA, whereas no CSA was produced by T cells or B cells under normal conditions. All the three cell populations released GM-CSA when activated by mitogen stimulation. Monocyte-derived GM-CSA production was greatly enhanced by zymosan (Zym), lipopolysaccharide (LPS) and concanavalin A (Con A), resulting in an augmentation approaching 3 to 4 times the untreated control. For T lymphocytes, the most contributive stimulants to induce GM-CSA release were phytohemagglutinin (PHA) and Con A, while Zym and LPS were not effective. B lymphocytes, after treatment with pokeweed mitogen (PWM) or PHA, were also capable of releasing large amounts of GM-CSA with a peak level near to PHA-stimulated T lymphocytes. The finding suggested that, when activated, B cells may participate in the inflammatory response and in the regulation of granulopoiesis.(ABSTRACT TRUNCATED AT 250 WORDS)