Lubeluzole is a neuroprotective compound in the final stages of clinical evaluation. We evaluated the effect of intravenous followed by intraperitoneal doses of lubeluzole on histological outcome after reversible tandem middle cerebral/common carotid artery occlusion in Long-Evans rats, with particular emphasis on the time window of efficacy. Lubeluzole, started 15 min after the onset of ischemia, had no adverse physiological or behavioral effects and reduced maximal infarct volume produced by 120 min or more of arterial occlusion by approximately 50%, from 143.2 +/- 11.8 to 73.3 +/- 18.4 mm(3) (p < 0.05). Lubeluzole did not prolong the duration of middle cerebral artery occlusion which could be tolerated before histological damage occurred. Lubeluzole was still effective if started 30 min after the onset of ischemia (34% reduction of maximal infarct volume; p < 0.05), but not after delays of 60 or 120 min. We conclude that lubeluzole has promise as a neuroprotective drug, particularly for more severe strokes, but must be started very rapidly after the onset of ischemia to be effective. Copyright (C) 1996 Elsevier Science Ltd