Host´s defense against external challenges activates an inflammatory response which is regulated by a set of chemical signals, including hormones. These immunomodulatory hormones, such as corticosterone, testosterone, and melatonin, trigger the systemic immune responses which are responsible for inflammatory assembly and resolution. The aim of this study was to investigate the effects of an immune challenge on endocrine and innate immune responses in the Bullfrog (Lithobates catesbeianus). Adult males were intraperitoneally injected with LPS (2 mg/kg) or saline and blood samples were collected 6 and 24 hours after injection for measurement of neutrophil/lymphocyte ratio, blood leukocyte phagocytosis, plasma bacterial killing ability and plasma levels of corticosterone, melatonin, and testosterone. Our results showed LPS-induced increased neutrophil/lymphocyte ratio and leukocyte phagocytosis, as well as, decreased melatonin and testosterone plasma levels, which were more pronounced 24 h after injection. Overall, we conclude that LPS intraperitoneal injection is able of activating innate immune response and modulating the hormonal profile of the Bullfrogs, with effects more pronounced 24 h than 6 h after treatment.