1. This study describes the changes observed in the rat microcirculation in vivo in the transparent tissue chamber of the rat back, during the florid hypertension produced by ligation of the rat aorta between both renal arteries.
2. Besides providing a new model for analysis of the action of therapeutic agents in hypertension, direct evidence of the variation in blood flow in hypertension is discussed. Fixation of the chamber tissues allows direct ultrastructural correlation with the altered function of particular vessels observed and recorded cinemicroscopically in vivo.