Studies were conducted to investigate the effect of reduced food intake on pituitary gonadotropin-releasing hormone (GnRH) sensitivity as a possible link in the delay of puberty by underfeeding. Immature female rats (30-32 days old at the start of each experiment) were used throughout the study. Rats on reduced food intake (R) received 60% of normal food intake beginning at the age of 21 days, whereas control (C) animals were fed ad libitum. In ovariectomized (OVX), estradiol benzoate-progesterone-treated R rats, low doses (less than 5 ng/100 g body wt) of GnRH injected intravenously produced higher serum luteinizing hormone (LH) concentration than in comparable C rats. No difference was found at 5 ng GnRH but response to high doses (15 and 45 ng/100 g body wt) was sharply reduced in R rats. No difference in serum follicle-stimulating hormone concentrations was found. In contrast to the OVX-steroid treated animals, in intact R rats, GnRH evoked higher serum LH concentrations at both low and high doses. These studies indicate that reduced caloric intake can affect pituitary GnRH sensitivity and that the effect depends on both the dose of GnRH and the internal, gonadal steroid hormone milieu.