Recent pilot studies in our laboratory have suggested that the attainment of female puberty and the subsequent reproductive success in the adult female saddle-back tamarin (marmoset) Saquinus fuscicollis, are influenced by the living conditions. Dominant females seem to be suppressing the onset of puberty and ovarian cyclicity in their subdominant females. Priming pheromones may be involved in mediating some of these effects. The proposed studies aim at elucidating some of the hormonal and possible pheromonal events and mechanisms involved in this effect. Preliminary data point at the possibility that one of the active mechanisms may be analogous to the human birth control pill of the progestin/estrogen composition. If so, the saddle-back tamarin will become an excellent model fo the neuroendocrine studies of this technique. The hormonal status of subdominant females will be monitored under various experimental conditions, using non-invasive techniques (urinalysis). One group of young adult females will be subjected to odors transferred from their mothers; another group will be under the influence of ovariectomized mothers either treated with estrogens or controls. Studies on the involvement of gonadotrophic hormones in the reproduction suppression phenomenon, and on the biosynthesis of steroids by gonads of subdominant females, will complement the previous observations.