Description: The present study was conducted to detect the direct relationships between melatonin and corticosterone under stress condition and possible actions of the two hormones on phagocytic activity of rat peritoneal macrophages. Two experiments were performed. In the first one stress increased the corticosterone plasma concentration to 276 с 25 ng/mL while nocturnal melatonin levels were depressed. In the second experiment, a clear rise in macrophages capacity to ingest latex beads was noticed when they were incubated with maximum melatonin quantity added (115 pg/mL) and combinations of melatonin and corticosterone investigated. The results concerning phagocytic efficiency showed that the only significant differences were when phagocytes were received from unstressed rats