The influence of the order of bleeding on corticosterone release in the mouse was examined. Female C57/BL6 mice were housed in groups of five animals in a low noise environment. After 10 days, they were successively captured and sacrificed every 2 minutes. The corticosterone levels increased in the fourth and fifth mice in a cage, i.e. within the time intervals from 4 to 6 minutes and from 6 to 8 minutes after the capture of the first animal. These results suggest that quiescent corticosterone levels can be measured only when the blood samples are obtained within 4 minutes following the capture of the first mouse.