The effect of age and physical activity stress (swimming until exhaustion) on the phagocytic capacity of the peritoneal macrophages was studied in young (12 +/- 4-week-old) and old (68 +/- 6-week-old) BALB/c mice. The attachment and ingestion of opsonized Candida albicans as well as the ingestion of inert particles (latex beads) by these cells was compared between young and old animals at rest. The results show that phagocytosis of peritoneal macrophages is not impaired in old mice. With respect to the effect of physical activity stress, we evaluated the phagocytic capacity both of C. albicans and of latex beads before and immediately after swimming until exhaustion, and in the absence or presence of a previous period (1 month) of training. The results indicate that the phagocytic capacity of peritoneal macrophages is increased after swimming until exhaustion, both with and without previous adaptation or training, and in both young and old mice.