Changes in leukocyte subpopulations and the effects of high-dose corticosteroids (HDC) on these changes were studied in patients undergoing total hip replacement surgery. Twelve patients were randomly divided into a non-steroid (n = 6) and a steroid group (n = 6). The steroid patient group was treated with HDC. In the non-steroid group, we found a leukocytosis, monocytosis, lymphocytopenia and granulocytosis after surgery in local anaesthesia. Only the changes in granulocyte counts were significant. Furthermore, the relative proportion of pan T-cells, helper/inducer T-cells, suppressor/cytotoxic T-cells, B-cells, activated T-cells and natural killer-cell subset did not change significantly during the post-operative course. Thus, lymphocytopenia was caused by reduced absolute counts of all these subsets. However, there was a tendency for decreased relative proportions of pan T-cells, inducer/helper T-cells, activated T-cells and natural killer (NK) cell subset in the early postoperative phase. Treatment with HDC significantly raised the numbers of leukocytes and granulocytes and decreased the lymphocyte and monocyte counts in the first 2 days after surgery, accounting for significant differences between the two patients groups. The percentage of pan T-lymphocytes was significantly lower in the steroid patient group on days 1 and 2 after the operation. There was no significant difference between the two patient groups with regard to the percentages of B-lymphocytes, T-lymphocyte subsets, NK cell subset, leu M3 cells and helper:suppressor ratio.(ABSTRACT TRUNCATED AT 250 WORDS)