These experiments were conducted sequentially in two parts. In the first, we examined the effect of frontal hypothalamic deafferentation (FHD) on photoperiod-induced changes in luteinizing hormone (LH) concentration in ovariectomized ewes (‘steroid-independent’ changes). In the second we placed Silastic implants of estradiol-17β in these same ewes and examined the effect of FHD on photoperiod-induced changes in the LH concentration in the presence of estradiol (‘steroid-dependent’ changes). 15 ovariectomized Suffolk ewes were subjected either to FHD (n = 10) or sham FHD (n = 5). They were placed in a photochamber and exposed to the following lighting regimens. In the first part, two trials of alternating lighting periods were used: trial 1 = 120 days of 8 h light (L):I6 h dark (D) followed by 90 days of l6L:8D; trial 2 = 90 days of 8L:I6D followed by 60 days of l6L:8D. In the second part, three lighting periods of alternating daylengths were used: 65 days of l6L:8D, followed by 60 days of 8L:I6D and by 60 days of l6L:8D. Blood samples were collected from the jugular vein at 20-min intervals for 3 or 4 h during the last day of each lighting period. Data on mean LH concentrations were obtained. The location of the FHD was verified histologically. In the absence of gonadal steroids, l6L:8D increased, whereas 8L:I6D decreased the LH concentration (p < 0.001) in both sham FHD and FHD ewes. In the presence of estradiol, the LH concentration in sham FHD ewes was 1.53 ± 0.94 ng/ml under l6L:8D, increased to 6.89 ± 4.04 under 8L:I6D, and returned to 0.72 ± 0.14 ng/ml under l6L:8D. In contrast, the LH concentration in FHD ewes was 1.45 ± 0.28 ng/ml under l6L:8D, decreased to 0.82 ± 0.17 under 8L:I6D, and further decreased to 0.54 ± 0.02 ng/ml under l6L:8D. These findings suggest that disruption of the direct neural connections between the anterior and mediobasal hypothalamus did not disrupt steroid-independent photoperiod-induced changes of the LH concentration, but prevented estrogen-dependent photoperiod-induced changes of the LH concentration. These results suggest that direct neural pathways between the anterior and mediobasal hypothalamus are essential for normal photoperiod-induced changes in LH secretion in the ewe and are compatible with hypothesis that the neural pathways which mediate steroid-independent and steroid-dependent changes may no