Sexual interaction between oppositely sexed pairs of rhesus monkeys depends upon a multiplicity of factors, but important among these is (1) the state of female receptivity and related to this, but independent of it, (2) female attractiveness as a sexual stimulus to the male. Female receptivity. Ovarian hormones appear to influence female proceptive behaviour (behaviour shown by the female which is likely to initiate copulatory or mounting activity in the male) and not unreceptiveness, as evidenced by changes in the female monkey’s active participation in sexual interactions during the follicular and especially mid-cycle periods. Ovariectomy reduces this proceptive behaviour but fails in the short term to induce unreceptiveness, which only becomes apparent following adrenalectomy. Adrenal androgens are important for full receptive behaviour in the female primate since adrenalectomised females become less unreceptive and more proceptive following administration of either subcutaneous testosterone or by implants of testosterone localized in the anterior hypothalamus. Thus, while the ovarian hormones are primarily involved in the female’s proceptive behaviour, adrenal’androgens are important for receptive behaviour and, in their absence, elements of unreceptive behaviour occur. Female attractiveness. The female primate will permit the male to mount throughout her menstrual cycle, and changes in the sexual interaction which occur during the menstrual cycle are strongly influenced by changes in the stimulus value of the female. Olfactory cues have been shown to be of importance in communicating the sexual attractiveness of the female rhesus monkey, oestrogen enhancing attractiveness and progesterone diminishing attractiveness. However, the behavioural response of males to odour cues concerning female attractiveness varies among individuals and, in a social context, past experiences and partner preferences readily modify the kind of behavioural response obtained. In this respect, the olfactory system appears to have a dual role in sexual interactions being concerned with both male sexual arousal and performance, and this, in turn, may be subserved by separate neural pathways between the olfactory bulbs and anterior hypothalamus. NESTING BEHAVIOUR OF THE DOMESTIC HEN D.G.M. WOOD-GUSH and M.J. GENTLE ARC Poultry Research Centre, West Mains Road, Edinburgh (Great Britain)