Dilute solutions of formalin, surgically injected under direct vision into the cortex of the mouse kidney is soon attended by degeneration and necrosis of the proximal convoluted tubules for a distance around the injection site. After 4 weeks, regeneration and some attempt at repair become evident in the epithelium. Although this experimental model represents a direct approach to the kidney, it is suggested that repeated renal exposure to small amounts of formalin, employed in commercial and scientific endeavors, which gain entrance to the circulation through minute breaks in the epidermal surface or the respiratory mucosa may eventuate in similar alterations of the human kidney.