The incidence of ovulatory disturbances in student nurses living in a restricted circumstance was evaluated by observing a basal body temperature (BBT) chart recorded for three to nine months by all of the student nurses in our medical college. The students were 18-21 years of age and were all living in a school dormitory. One hundred of the 154 students (64.9%) were anovulators during the school term. However, 40 of the anovulators showed ovulatory cycles with biphasic BBT patterns during their spring and/or summer holidays. The subjects' living conditions were investigated by questionnaire. Age of menarche, sport activity, self-perceived physical and mental work load, and native region did not appear to be related to their ovulatory disturbances. Weight-height-derived indices indicated that the anovulators had a tendency to corpulence as compared to the regular ovulators. Serum luteinizing hormone, follicle stimulating hormone, and prolactin levels of the anovulators were not significantly different from the regular ovulators.