The aim of this article was to evaluate the physiological significance of tumor necrosis factor-alpha (TNF-alpha) in seasonal accumulation of adipose tissue, hyperinsulinemia, and anovulation in Scotophilus heathi. The result showed seasonal variations in the circulating TNF-alpha level. A higher level of circulating TNF-alpha was observed during quiescence and recrudescence, whereas a lower level of TNF-alpha was observed during winter dormancy and the preovulatory period. An increased circulating TNF-alpha level coincided closely with accumulation of adipose tissue and hyperinsulinemia. Immunocytochemical localization of TNF-alpha in the ovary showed immunoreactivity mainly in the oocytes and theca-interstitial cells. The oocytes of small and medium-sized follicles showed strong TNF-alpha immunostaining, whereas weak immunoreactivity was observed in the large antral follicles. The atretic follicles showed mild TNF-alpha immunostaining. TNF-alpha immunoreactivity in the ovary was slightly higher during the quiescence and preovulatory periods compared with the periods of recrudescence and winter dormancy. TNF-alpha alone significantly increased androstenedione and estradiol production by the ovary in vitro but did not augment the luteinizing hormone (LH)-induced androstenedione production. However, TNF-alpha did augment LH-induced estradiol production. The results of this study suggest the involvement of TNF-alpha in the interaction among adipose tissue accumulation, insulin resistance, and ovarian activity in S. heathi.