It has been shown that some antibiotics can modify cytokine production. We have examined the effect of rifampicin on secretion of interleukin-1beta (IL-1β), IL- 6, IL-10, and tumor necrosis factor alpha (TNF-a) by lipopolysaccharide (LPS)-stimulated or heat killed staphylococci (Pansorbin) stimulated monocytes. Secretion of IL-1β and TNF-a were significantly inhibited (P<0.002) whereas secretion of IL-6 and IL-10 were significantly increased (P<0.003) by rifampicin treated mononuclear cells. Rifampicin had immunomodulatory effects through its capacity to alter the secretion of tested cytokines by human monocytes.