Neutrophils (PMN) have been implicated as mediators of the reperfusion injury which occurs in skeletal muscle after ischemia. This study was performed to measure PMN phagocytosis and chemotaxis after 3 hr of ischemia followed by 1 hr of reperfusion in a model where a significant reperfusion injury occurred. Baseline blood samples were drawn from an ear artery from New Zealand white rabbits for PMN and serum. The right iliac and femoral arteries were clamped for 3 hr which resulted in a severe clinical reperfusion injury. Just prior to clamp release, blood was harvested from the right iliac vein. After 1 hr of reperfusion, blood was again harvested from the right iliac vein. Phagocytosis was measured by the percentage ingestion of zymosan beads by the PMN. The zymosan beads had been opsonized with baseline (b), ischemia (i), or reperfusion (r) serum. Results for phagocytosis revealed no difference for (b) PMN when opsonized by (b), (i), or (r) serum. A significant increase was seen in (i) PMN phagocytosis when (i) or (r) serum was present. Also, a significant increase in (r) PMN phagocytosis was seen when (i) serum was present (ANOVA: F = 14.47; P = 0.0002). Chemotaxis was evaluated by the number of PMN migrating across a filter. Serum obtained from (b), (i), and (r) blood samples served as the chemoattractants. Significant increases in chemotaxis were observed for (b), (i), and (r) PMN when (i) serum was used as the chemoattractant (ANOVA: F = 7.11; P = 0.0025). We conclude: (1) Rabbit PMN harvested after ischemia and reperfusion demonstrated increased phagocytosis when (i) serum was present.(ABSTRACT TRUNCATED AT 250 WORDS)