The usefulness of single, random measurements of serum FSH and LH in the diagnosis of amenorrhea was investigated. These determinations were performed upon 146 unselected subjects. A wide range of values was found. In primary amenorrhea, normal values were helpful in excluding hypogonadotropic hypogonadism. Low values were not proof of hypogonadotropic hypogonadism, since some subjects could be stimulated by clomiphene to secrete increased amounts of FSH and LH. High values were found in patients with gonadal dysgenesis or unexplained ovarian failure. In secondary amenorrhea, high values were useful in detecting ovarian failure or early menopause. In the remaining subjects, there was no strong correlation between these measurements and the clinical classification of amenorrhea.