The authors report two cases of menstrual irregularities associated with bupropion treatment. This is the first report of such an association, and it is supported by data collected by the Burroughs Wellcome Co. Since the mode of action of this effective new antidepressant is basically unknown and does not operate through any of the putative mechanisms of the classical antidepressants, its side effect profile is of heuristic as well as practical importance.