25-day-old female rats were left intact, or rendered either blind-anosmic or blind-anosmic-pinealectomized. Five weeks later, blind-anosmic animals were found to possess significantly depressed body, anterior pituitary, uterine and ovarian weights. The pituitary levels of LH were elevated while pituitary prolactin was depressed in the dual sensory-deprived rats. Blind-anosmic animals also had significantly depressed plasma levels of LH and elevated plasma levels of prolactin. The effects of blinding and anosmia were effectively reversed by pinealectomy. Ovariectomized, estrogen and progesterone-treated (OVX, EP-treated) rats that received an intracarotid injection of a medial basal hypothalamic (MBH) extract from intact or from blind-anosmic-pinealectomized female rats exhibited a marked rise in plasma LH to a peak at 10 min after injection. This peak was followed by a steady decline in plasma LH concentration. Animals injected with MBH extract from blind-anosmic rats also demonstrated a rise in plasma LH with the levels remaining more or less constant for the 10 and 20-min samples. Rather than declining, the plasma LH levels in 3 out of 4 rats exhibited a further increase until the 40-min sample. The injection of either cortical extract or saline had no effect on plasma LH levels. OVX, EP-treated rats receiving either MBH extracts from intact or blind-anosmic rats or cortical extract exhibited a depression in plasma prolactin titers 5 min following injection. This response was followed by a slight increase in plasma prolactin at 10 and 20 min with a subsequent decrease. Each of the OVX, EP-treated recipients injected with MBH extract from blind-anosmic-pinealectomized rats responded with an obvious increase in plasma prolactin levels within 5 min after injection, followed by a decrease. It was concluded that the MBH of the blind-anosmic rat was high in LRH activity while PIF appeared to predominate over PRF activity. On the other hand, in the MBH of the blind-anosmic-pinealectomized rat, LRH activity was lower while PRF appeared to predominate over PIF activity.