Abstract:In order to find out which factor, genetic or environmental, is more involved in determining hand usage, the distribution of handedness in Japanese senior high school students and the success of their parents' attempts at conversion of handedness was investigated with respect to four pairings of parental handedness. When a child's handedness was related to that of the parent, children of a left‐handed parent were more likely to be non‐right‐handed than those of both right‐handed parents. There was no significant relation between parental handedness and the rate of handedness conversion of children. The results are in favor of the view that human handedness is genetically rather than forcibly determined by parents, although environmental factors such as parents' interference are involved in decreasing the incidence of non‐right‐handedne