Fifteen wild-caught iguanid lizards (14 Sceloporus variabilis and one S. malachiticus) were used in a 3 mo study on thermal acclimation. Over a 2 mo period, five of the lizards showed decreased activity, anorexia and enlarged joints, and were either found moribund or were euthanatized due to their poor condition. Specimens taken from lesions in four of the five lizards were cultured and were infected with Salmonella spp. Salmonella spp. was cultured from cloacal swabs in six of the 10 surviving lizards. Standard metabolic rates of those that were infected did not differ significantly from those that were not infected. We postulate that the lizards were inapparent carriers of Salmonella spp. at the time of capture and, as a result of stress, five developed active overwhelming systemic infections.