The ontogeny of oxytocin receptors in rat forebrain was studied using the selective oxytocin receptor antagonist 125I-d(CH2)5[Try(Me)2, THR4, Tyr-NH29]OVT ([125I]-OTA). With in vitro receptor autoradiography, binding was noted on the first postnatal day in dorsal subiculum and thalamus. On postnatal days 5–18, intense labeling was evident in posterior cingulate cortex, dorsal subiculum, lateral septum and the CA1 subfield of hippocampus. Of these regions only the lateral septum expressed oxytocin receptors in adult brain. Competition studies on coronal sections through posterior cinguulate, septum, and dorsal subiculum at P10 demonstrated that transient binding sites in these areas were indeed oxytocin selective (OXY>AVP>V1V2). Results of saturation studies on cingulate membranes from 10-day-old pups agreed favorably with previous reports of the kinetics of [125I]-OTA binding to adult oxytocin receptors (Kd = 0.1 nM in P10 cingulate cortex vs. 0.07 nM for adult ventral subiculum). In contast to these evanescent developmental sites, oxytocin receptors in the bed nucleus of the stria terminalis and the ventromedial nucleus of the hypothalamus only appeared in adulthood, presumably in response to the surge of gonadal steroids at puberty.