Summary.A clear sex difference in behavior in standing equilibrium has been observed. Swaying in young women is significantly wider than that in young men, and the numbness of the soles due to standing in ice water and closing the eyes noticeably increases swaying in women, but not in men. This difference between the sexes and some other observations on the maintenance of standing equilibrium can be explained by the following hypothesis: If muscular strength is great, muscular myotatic stretch reflexes are used almost exclusively in the maintenance of standing equilibrium, and in this case the amplitude of swaying is small. If muscular strength is not great, other afferent parts, the soles and sight