Detection of circulating levels of gonadotropin is fundamental in reproductive physiology and related disorders. The advent of monoclonal antibodies might supply the clinician with faster and more accurate estimates of these hormones. We have evaluated the hormonal determinations provided by a monoclonal assay and those generated from our previous assay, produced by the same manufacturer, based on polyclonal antibodies. Comparison was performed on blood samples collected from volunteers with regular menstruation (n = 51) or patients attending our Clinic. The correlation between data provided by the two assays fluctuated from the almost complete overlap of the physiological menstrual cycle to the striking dissociation of the patients (n = 13) receiving a Gonadotropin Hormone-Releasing Hormone analog for gonadotropin suppression. Intermediate coefficients of correlations were recorded in normal subjects undergoing a Gonadotropin Hormone-Releasing Hormone stimulation test (n = 12) and in patients with functional hypothalamic amenorrhea (n = 19) or polycystic ovarian disease (n = 37). Values obtained with the monoclonal assay tended to be lower than those recorded with the previous system. A closer correlation with the clinical findings was observed in the hormonal values originated with the monoclonal assay.