The neuroprotective effects of recombinant neutrophil inhibitory factor (NIF) have been assessed with temporary (2 h) middle cerebral artery (MCA) occlusion in the rat using the intraluminal suture technique. Administration of NIF (1.5 mg/kg, i.v.) immediately after the onset of reperfusion and at 4 and 6 h post-MCA occlusion significantly reduced both hemispheric infarct volume (P < 0.001) and brain swelling (P < 0.001), and improved neurological outcome (P < 0.02) when assessed at 24 h. These results demonstrated the marked neuroprotective efficacy of NIF in a rat model of transient focal cerebral ischaemia.