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-17 beta 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):16 h dark (D) followed by 90 days of 16L:8D; trial 2 = 90 days of 8L:16D followed by 60 days of 16L:8D. In the second part, three lighting periods of alternating daylengths were used: 65 days of 16L:8D, followed by 60 days of 8L:16D and by 60 days of 16L: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, 16L:8D increased, whereas 8L:16D decreased the LH concentration (p less than 0.001) in both sham FHD and FHD ewes.(ABSTRACT TRUNCATED AT 250 WORDS)