Multiple factors can impact the immune function of ectotherms, including hormone levels, seasonality, sex, body condition, and body temperature. We investigated the seasonal covariation of steroid levels (testosterone for males, estradiol and progesterone for females, and corticosterone for both sexes), immune parameters (total and differential number of leukocytes, plasmatic bacterial killing ability), body condition index, and body temperature in males and females of the tegu lizard (Salvator merianae). This species displays pronounced transitions in life-history stages along the year: reproductive period, non-reproductive period, and hibernation. We expected immunity to be correlated with body temperature, steroid levels, and body condition. We also expected lower immunocompetence during hibernation compared to the other life stages. We observed a positive correlation between the differential number of leukocytes and body temperature experienced one-week prior to sampling. On the other hand, BKA and the total number of leukocytes were not influenced by body temperature, indicating that some immune traits are viable under a wide range of temperatures. Against our hypotheses, there were no correlations between hormone levels, body condition, and immune traits. Also, immune parameters did not decrease during hibernation. Our data indicates how important is to understand the relationship between body temperature and immune response in ectotherms, especially in a climate change scenario. The lack of correlations between immune variables, hormones levels, and body condition emphasize that patterns of variation in immune response in reptiles can depend on the species, immune parameters analyzed, and other ecological traits.