Summary. Prepubertal gilts were fitted with jugular vein and carotid artery catheters at 148 days of age. At 160 days of age the 24 gilts were allocated to treatment in a 2 × 2 factorial design involving intra-carotid infusion of cortisol (10 mg in 40 ml saline) or saline alone with or without i.v. injection of 5 μg synthetic GnRH midway through the 1 h infusion. Plasma cortisol concentrations were elevated in gilts infused with cortisol (P < 0·05). The LH response to exogenous GnRH was reduced by cortisol infusion. Treated gilts released less LH (P < 0·001) and had a lower mean LH peak (P < 0·01) than did control gilts but the timing of the induced LH peak was not affected. In the absence of an exogenous GnRH challenge, cortisol infusion increased the endogenous secretion of LH (P < 0·01). These results suggest that acute elevations in plasma cortisol concentration may be involved in mediating changes in pituitary responsiveness and the secretion of LH in the peripubertal gilt.