Plasma melatonin, LH, FSH, PRL, and corticoids were measured in two patients with pineal tumors. Plasma melatonin was not detectable (less than 7 pg/ml) in either patient while gonadotropin and cortisol levels were within the normal range. One patient exhibited low PRL levels and the other patient, a prepubertal boy, had elevated levels. The clinical value of the measurement of melatonin as a potential marker for all pineal tumors must be questioned.