Cochlear blood flow (CoBF) and endolymphatic sac (ES) blood flow (ESBF) were measured in different groups of guinea-pigs by laser-Doppler flowmetry after the intravenous administration of various drugs through the jugular vein for 60 sec. These drugs included 50% glycerol, 70% isosorbide, 20% mannitol, 7% sodium bicarbonate and 1% diphenidol. For CoBF measurements, a probe was positioned on the basal turn of the right cochlea via a ventral approach. For ESBF measurements, it was placed on the right ES through the posterior cranial fossa via a dorsal approach. The average initial measured value of ESBF (8.31 +/- 2.97 ml/min/100 g) was significantly greater (p < 0.0001) than that of CoBF (4.33 +/- 1.15 ml/min/100 g). Following administration of most drugs except for diphenidol, both CoBF and ESBF increased immediately after administration; however, following diphenidol administration both CoBF and ESBF decreased. The magnitude of the CoBF response tended to be greater than that of the ESBF response (p = 0.006-0.112). It seems likely that this reflects anatomical differences in the vascular supplies, i.e. CoBF from the vertebrobasilar artery and ESBF from the external carotid artery. In addition, the presence of micropores or fenestrations in the ES vasculature may contribute to the differences between CoBF and ESBF.