Previous experiments have demonstrated that the cholinergic compounds pilocarpine and oxotremorine decrease the oestrogen plus progesterone-activated lordosis response in the female rat. The present study showed that pilocarpine and oxotremorine, in doses which did not interfere with overt behaviour, also facilitated the lordosis response when given 48 h after oestrogen and thus substituted for the progesterone treatment. This effect could be counteracted by atropine but not by methylatropine pretreatment. The facilitating effect was not obtained after adrenalectomy or hypophysectomy. It is therefore suggested that the facilitating effects of the cholinergic compounds on copulatory behaviour in the oestrogen-treated female rat is mediated by pituitary—adrenal mechanisms.