Effects of melatonin ( MT ) and supernatants from cultured pineal glands stimulated by 10 ?mol/L isoproterenol (ISO) for 0, 30, 60, 120 min on interleukin I ( IL-1 ) production by peritoneal macrophage ( PM? ) in rats were studied. Theses results showed that LPS-induced IL-1 production by PM? was enhanced by in vitro treatment with MT (0.1~1 ?mol/L ) , but IL-1 production was not influenced by MT without LPS. LPS-induced IL-1 production by PM? was enhanced in various degree by the supernatants, action of supernatants for 60min was best. The data is suggested that LPS-activated M?s may be one of target cells for MT.