PU.1 is a transcription factor found in macrophages, B cells, neutrophils, and hemopoietic stem cells. In macrophages PU.1 regulates a number of genes, includingc-fms,CD11b, CD18, and FcγR1b. Previously, in primary macrophages PU.1 binding to the sequence GAGGAA was found to be induced by treatment with bacterial lipopolysaccharide (LPS) and interferon-γ (IFN-γ). Here we investigated the role of protein kinase C (pKC) in the induction of PU.1 binding in macrophages. We report that pharmacological activation of pKC increases PU.1 binding, while inactivation of pKC inhibits the increases in PU.1 binding by agents which activate pKC in macrophages (LPS and tumor necrosis factor-α), but not by an agent which does not activate pKC (IFN-γ). pKC activation may therefore be one pathway by which PU.1 binding may be increased in primary macrophages.