Stress and depression are associated with a variety of alterations in the endocrine and immune systems. Leucocyte adhesiveness/aggregation (LAA) has recently been proposed as a simple indicator of stress in humans. The objective of the present study was to examine the serum concentration of corticosterone, neutrophil phagocytosis, lymphocyte proliferation, LAA and differential white blood cell (WBC) count in rats at different time intervals following an exposure to the behavioural despair and 'open field' tests. Thirty min following exposure to the behavioural despair test, the concentration of corticosterone was significantly elevated. An increase in the percentage of neutrophils and LAA, and a decrease in the percentage of lymphocytes and monocytes in the WBC count, were also found 30 min and 60 min after exposure to both the behavioural despair and 'open field' tests. A reduction in neutrophil phagocytosis was also observed 60 min after the exposure to these situations. The results show that there are endocrine and immune changes following exposure to these experimental situations. LAA appears to be a particularly useful indicator of acute stress in rats.