This study investigates the validity in Japan of union participation models developed in North America. The results of ordinary least squares analysis suggest that members' participation in unions is positively related to many of the same factors in Japan as in North America: for example, length of union membership, pay, dissatisfaction regarding pay and working conditions, degree of interaction with others in the work group, and perceptions of the union's effectiveness and its democratic character. Some findings at odds with those of Western studies, however, are that older workers and better-educated workers are less (rather than more) likely than others to actively participate, and job status is unrelated (rather than positively related) to participation.