We investigated the relation between heterophil/lymphocyte ratios, hepatozoon parasitemia, and two presumed fitness correlates (residual body condition and growth rate) in two regional populations of the Eastern Foxsnake, Pantherophis gloydi. Parasite intensity was not related to either fitness correlate. We found a significant relationship between log (heterophil to lymphocyte [H/L] ratio) and residual growth rate for individuals from Georgian Bay, but not those from southwestern Ontario. There was no significant relationship between log (H/L ratio) and residual body condition in either regional population. We also detected dramatic differences in parasite prevalence and H/L ratios between the two populations: Almost half of the sampled individuals from Georgian Bay were infected with hepatozoons compared to only 2 of 46 infected individuals from southwestern Ontario; H/L ratios were significantly higher in Georgian Bay individuals implying that individuals in this northern population experience higher levels of stress than those in southern Ontario where the environment differs markedly.