The effects of comparable lower-limb eccentric exercise that induces high (bench-stepping; STEP) and low (repeated eccentric muscle action; ECC) systemic stress on neutrophil and monocyte phagocytic and respiratory burst activity, and activation antigen (CD11b, CD66b, CD64) expression, were compared in recreationally active subjects (20-37 years old). Leucocyte responses were determined before and 4, 24, 48 and 72 h after exercise using whole-blood flow cytometry. Serum creatine kinase (CK) activity and perceived muscle soreness [delayed-onset muscle soreness (DOMS)] were assessed at the same time points up to 96 h; as a control, measurements were taken during 5 days of rest. DOMS in quadriceps and contralateral triceps surae peaked 24-72 h after STEP (P <0.05) and 48-72 h after ECC (P <0.05), whereas serum CK activity (mean+/-S.E.M.) was only higher than baseline after ECC (15,123+/-3,488 at 96 h compared with 115+/-29 units x l(-1) pre-exercise; P <0.01). The total leucocyte count increased from (5.4+/-0.4) x 10(9) x l(-1) and (5.7+/-0.5) x 10(9) x l(-1) at baseline to (7.6+/-0.5)x10(9) x l(-1) and (7.0+/-0.5) x 10(9) x l(-1) at 4 h after STEP and ECC respectively; this was largely attributable to changes in the neutrophil count (P <0.05). The proportion of neutrophils undergoing phagocytosis and respiratory burst was unchanged 4 h after ECC and STEP, which, given the increase in neutrophil count after exercise, would suggest an overall improvement in systemic neutrophil microbicidal potential. The intensity of neutrophil (P =0.01) and monocyte (P <0.05) phagocytosis and neutrophil respiratory burst responses (P <0.05) was only increased 24 h after STEP, whereas no changes in these measures were observed after ECC. Activation antigen expression was unchanged in all groups. These findings suggest that systemic stress evoked during an acute bout of eccentric exercise has a greater influence on subsequent leucocyte functional responses than the degree of muscle damage induced.