A possible explanation for the normal prolactin serum levels in the seven reported patients with normal fasting prolactin values and described “galactorrhoea-endometriosis syndrome” could be the possibility of nocturnal hyperprolactinaemia: in such patients, the nocturnal prolactin peak is more exaggerated than the physiological prolactin peak during nocturnal sleep. Here, PRL is linked to Increased circulating prolactin concentration.