The hypothalamic - pituitary - gonadal axis was evaluated in men with paedophilia and non-paedophilic paraphilia, and in normal male controls, by infusion of 100 mcg. of synthetic luteinising hormone-releasing hormone (LHRH). There were no significant differences among groups in age, height, weight, testosterone, baseline luteinising hormone (LH) and follicle stimulating hormone (FSH), and FSH response to LHRH. However, there was a significant difference between the paedophilic group and the other two groups in the LH response to LHRH. The paedophiles responded with a marked elevation of LH, when compared with the non-paedophilic paraphiliacs and controls. These data indicate a hypothalamic - pituitary - gonadal dysfunction in paedophiles.