Previously, we found that murine bone marrow-derived macrophages (MO) induced in vitro by MO-specific colony-stimulating factor (M-CSF) have little capacity to release prostaglandin E2 (PGE2) and other eicosanoids. This work focused on the functional and transcriptional expression of the key enzymes for the PGE2 synthesis in the MO. Nonadherent bone marrow cells were cultured with RPMI1640 plus 10% fetal bovine serum (FBS) further supplemented with either M-CSF or granulocyte-macrophage (GM)-CSF and interleukin-3 (IL-3). Cellular PGG/H synthase (cyclooxygenase) levels were quantified by cytometric analysis with antibodies specific for the two isozymes of PGG/H synthase (PGG/H synthases 1 and 2). The enzyme activity was monitored by adding exogenous arachidonic acid (AA) substrate to the bone marrow MO cultures and to the cell-free particulate fractions. The levels of PGE2 converted were quantitated by radioimmunoassay (RIA). mRNA levels of the enzymes were detected by Northern blot analysis hybridized with mouse PGG/H synthase cDNA probes, 2.7 kb (PGG/H synthase 1) and 4.2 kb (PGG/H synthase 2). In addition, cellular phospholipase A2 (PLA2) activities were detected with sn-2–14C-arachidonyl phosphatidylcholine as a substrate. Cells proliferating in the presence of GM-CSF and IL-3 for more than 4 days showed significant release of PGE2 (> 7 ng/10(6) cells) when stimulated by AA. These cells also expressed significant amounts of PGG/H synthase 1 protein, its mRNA (2.7 kb) and cellular PLA2. M-CSF-induced MO, in sharp contrast, expressed little PGG/H synthase protein, mRNA, cellular enzyme activity, or PGE2 release, despite comparable levels of cellular PLA2 activity. These data suggest that the capacity of differentiating marrow-derived MO to form PGE2 is growth factor-dependent.