The study was designed to determine the influence of photoperiod on the nocturnal gene expression of proinflammatory cytokines such as interleukin (IL)-1β (IL1B), IL-6 (IL6), tumor necrosis factor α (TNF) and their receptors: IL-1 type I receptor (IL1R1), IL-6 receptor (IL6R), glycoprotein 130 (IL6ST), TNF type I and II receptors (TNFRSF1A and TNFRSF1B, respectively) in the pars tuberalis (PT) of ewe with the endotoxin-induced acute inflammation. The studies were performed on adult ewe (n = 24) in two photoperiods: long night (LN; 16:8; October) and short night (SN; 8:16; June). The animals from each photoperiod were divided into two groups: control (n = 6) and lipopolysaccharide (LPS)-treated (n = 6). All experiment steps were performed in the darkness. Two hours after the sunset the ewe received the intravenous injection of LPS or an appropriate volume of saline. Three hours after the injections all animals were slaughtered. It was found that melatonin concentration in control ovine serum was higher (P < 0.05) during LN than SN period. Endotoxin decreased (P < 0.05) the melatonin release only in ewe kept under SN condition. The transcripts encoding all examined proinflammatory cytokines and their receptors were expressed in the PT. Moreover, the PT collected from LPS-treated ewe during LN were characterized with higher (P < 0.05) expression of IL6, TNF, IL6ST, TNFRSF1A and TNFRSF1B genes compared with the tissues collected during SN. Similar influence of photoperiod was also observed in the case of TNF gene expression in the control sheep. Obtained results suggest that the PT may be one of the gateways for immune-endocrine interactions and these interactions may be affected by the photoperiod.