Effects of parathyroidectomy (PTx) in the rat at the 5th day of gestation on the functional development of gonadotrophin secretion in the infantile offspring was examined. A single subcutaneous injection of 10 micrograms/kg of luteinizing hormone-releasing hormone (LHRH) induced a significant increase in serum follicle stimulating hormone (FSH) and luteinizing hormone (LH) in control- and PTx-F1 male and female rats already at 3 days of age. The response in female rats was greater than in males at all ages examined. In the control- and PTx-F1 rats, age-related increase in the responsiveness to LHRH was observed in both sexes for LH but only in females for FSH. However, LH and FSH release by LHRH in the PTx-F1 female rats was significantly lower than that in control females at 14 and 22 days of age. In the PTx-F1 male rats, only FSH response to LHRH showed a tendency to decrease at 22 days of age. Serum calcium levels in 3-day-old PTx-F1 male and female rats were significantly lower than those in controls but only a slight decrease was observed in the PTx-F1 rats at other ages. The present results indicated that a low serum calcium environment during fetal life in the rat affects the functional development of pituitary responsiveness to LHRH, particularly in females.