The pathophysiology underlying the high incidence of post-stroke infectious complications has not been fully understood. We measured the respiratory burst of neutrophils as an index of their bactericidal function in patients with haemorrhagic stroke, and we also measured the plasma concentrations of noradrenalin, cortisol and neutrophil function-related amino acids. Blood samples were obtained from patients who underwent emergency craniotomies for haemorrhagic stroke (n=11) or CT-guided stereotaxic aspiration of intracerebral haematomas (n=6). Neutrophils were isolated, and their chemiluminescence response to N-formyl-methionyl-leucyl-phenylalanine was measured. Healthy volunteers served as controls (n=15). In patients with stroke, the chemiluminescence response of the isolated neutrophils was significantly lower than in the controls, and it was significantly inversely correlated with the plasma noradrenalin concentration. By Day 30, this value approached control levels. Other parameters measured were not significantly correlated with the chemiluminescence response. Stroke-induced suppression of the neutrophil respiratory burst may be responsible for frequent post-stroke infectious complications.