It is generally accepted that the pineal gland is a neuroendocrine organ. Several recent experiments have shown that the pineal gland has functional and anatomic connections with many organs and systems, particularly with the immune system, and, therefore, the gland is now recognised as an important immunoneuroendocrine organ both in man and animals. The present study investigates the effect of pinealectomy on some immune parameters including zinc pool alterations and wound healing process in different age group in rats and also investigates the effect of melatonin administration on wound healing in different age groups. Experiments were performed on two different age groups of rats (neonatal and young). We have experimentally shown the induction of immune depression by pinealectomy and the restorative competence of melatonin administration in the present study. The results also showed that the plasma zinc level was significantly reduced in the third week after the pinealectomy particularly in pinealectomised neonatal rats and the wound healing process affected only in pinealectomised neonatal rats but restored to normal by melatonin administration. In view of these data, as described previously, the pineal gland has a main regulatory function in immune physiology, but our study indicates that only neonatal immune functions are significantly affected by pinealectomy. (C) 2000 Harcourt Publishers Ltd.