Myohæmoglobin and the Crush Syndrome A COMMON type of air-raid casualty is the person who has remained trapped for several hours with a limb crushed or compressed beneath debris. Such patients, after their release and admission to hospital, frequently develop a characteristic set of symptoms which has been called the 'crush syndrome'. The most striking features of this condition, apart from surgical shock, are the excretion of myohæmoglobin in the urine and the onset of severe renal failure, which often ends in death from uræmia. Bywaters and Popjak (Surg. Gynec. Obst., 75, 612; 1942) attempted to reproduce this condition in rabbits by experimental crushing or compression of the leg muscles. They found that surgical shock ensued as in man, but there was no myohæmoglobinuria and no renal damage. The absence of myohæmoglobinuria was readily explained by the finding that rabbit's muscles contain practically no myohæmoglobin, and the results naturally suggested that the renal damage which occurs in man might in some way be caused by the renal excretion of myohæmoglobin. Bywaters and Stead (Quart. J. Exp. Physiol., 33, 53; 1944) have investigated this possibility and they find that while injection of myohæmoglobin into normal rabbits (with alkaline urine) does not damage the kidney, injection into rabbits with acid urine or into rabbits after limb crushing does produce severe kidney damage which may be fatal. It seems that in the crush syndrome both myohæmoglobin and various acid breakdown-products are liberated from the crushed muscle, and the excretion of myohæmoglobin in an acid urine is the main cause of the renal damage, though why myohæmoglobin should damage the kidney is not yet clear.