The Authors evaluate the variation of Sex Hormone Binding Globulin during the menstrual cycle in 17 normal menstruating healthy women. The resulting data seem to show not significant modification in the protein serum level, in agreement with most of the reports in literature. A possible explanation might be the insufficient length of estrogen stimulation in the prolipherative phase. This might lead to hypothesize that in presence of marked impairments of sex steroid metabolism SHBG levels may vary significantly.