The clinical usefulness of plasma LH and FSH radioimmunoassays, both in basal and dynamic conditions, is briefly discussed. While occasional LH and FSH determinations may indicate only a serious gonad failure, at least when high values are found, dynamic studies before and after LH-RH i.v. injection may suggest a hypothalamic or pituitary lesion. In this regard the LH-RH test is presented as the most evident demonstration of the utility of gonadotropin radioimmunoassay. Different patterns of response are presented and their correlation with menstrual disorders is discussed in view of different distribution (Tab.1). Moreover, the AA. suggest a primary hypothalamic deficiency in LH-RH in the cases of "deficient" response that, being a constant finding in different days, became a "normal" response after 3 days therapy with LH-RH infusion and returned to basal levels 2 months later. Equally, an "exaggerated" response consistenly found in some patients with secondary amenorrhea, is suspected to be of hypothalamic origin since "normalization" may be obtained after a similar LH-RH treatment.