Severe edema developed around the kidneys of rats after several days of uremia induced by large intravenous doses of mercuric chloride. Edema was prevented when the kidney was removed or had its hilum ligated, or when rats were deprived of fluid intake. The edema fluid had a very low protein content. These facts suggested that the edema was derived from the kidneys, probably from the glomerular filtrate, and that the edema depended on some degree of remaining renal function. Increased permeability of the necrotic proximal tubules and obstruction by casts in the collecting tubules may have been involved. Histologic study suggested that the fluid diffused through the intact renal capsule. These experiments provide a model for perinephric (perirenal) fluid accumulation in certain human diseases and in certain intoxications of grazing animals.