Following intraperitoneal injection of ethacrynic acid, progressive, mainly reversible changes occurred in the stria vascularis, affecting all three cell types and the capillary basal laminae. Both marginal and intermediate cells showed abnormalities early, at a time when EP was just beginning to decline. Progressive changes in marginal cells culminated in apical bulging followed by recession of the swelling and stretching of the cells concomitant with gross interstitial oedema. Marginal cell mitochondria showed damage and the transcellular tubule system was dilated. Intermediate cells also showed a progression of changes, culminating in a marked, but reversible, shrinkage. The time of appearance of severe strial derangement correlated with the time of maximal depression of EP. The ability of the stria to regain rapidly an almost normal morphology appeared to be due partly to the distribution and orientation of microtubules in marginal and intermediate cells preventing major disruption of stria vascularis architecture.