THE INFLATABLE plastic splint, which surrounds the extremity including the digits, is a good first aid measure for the immobilization of fractures but, when applied with an air pressure exceeding certain limits, may occlude the lumen of the small blood vessels of the digits. The risk of occlusion of the blood vessels becomes even greater in an extremity in which the blood supply is already impaired by disease or trauma. Effective immobilization of an extremity obtained by too high an air pressure may unwittingly lead to necrosis of the digits. A visual demonstration of the effect of various levels of air pressure on the circulation of the great toe was deemed advisable, therefore, to determine a safe but effective pressure for immobilization. Five normal individuals were studied and the results were similar. The results obtained in the reported instance are characteristic of all. Methods A transparent, inflatable plastic boot A transparent, inflatable plastic boot