Solow describes a female patient whose behavior and mental status fluctuates in a definite cycle: one period lasting about seven days resembles a mildly hypomanic phase and the other period lasting about ten days seems more of a schizophrenic nature. The entire cycle lasts about one month and has been observed to recur regularly in a closed hospital for some three years. External events or activities appear to have no effect on it. There is no apparent connection with the menstrual cycle. Solow reviews the literature describing similar cases but the etiology and dynamics remain obscure.