The stria vascularis (SV) was quantitatively compared in three species commonly used in auditory research: guinea pig, mouse and gerbil. Measurements were obtained for surface area, cross-sectional area, length, width and thickness of SV. Surface area and length were proportional to the overall size of the cochlea in each species, but there was no significant difference between species in mean cross-sectional area. In guinea pig and mouse, there was no significant difference in thickness (endolymphatic surface to spiral ligament) and a similar pattern was observed for width (Reissner's membrane to spiral prominence): the width of SV increased from the apical end to a point 80% of the distance from the apex, then decreased to the basal end of SV. The thickness of gerbil SV was significantly less (P less than 0.001) and there was less of a gradient in width as compared to guinea pig and mouse. The vessels of SV were compared in terms of vascular density (vessels per unit area), rbc density (red blood cells per unit area), R/V (rbc density/vascular density), inter-vessel spacing and vessel diameter. Highly significant (P less than 0.001) differences between species were found in vascular density, RBC density and vessel diameter, but there were no differences between species for R/V or inter-vessel spacing. The results of this study may reflect differences in the metabolic requirements of SV among different species.