Toxins of Xenopus laevis elicit gaping responses in some snakes, but introduced populations of this species in California provide an additional food source for Thamnophis hammondii with no observable ill effects to the snake. This study addresses the locomotor performance of T. hammondii after consuming this toxic frog. Endurance and speed of T. hammondii were measured along a 2-m long racetrack when subjects were not fed recently, when they were fed sunfish (Lepomis, a non-toxic prey), and when they were fed X. laevis. Snakes tended to be slower after eating, but ingestion of X. laevis did not affect either measure of locomotor performance in T. hammondii. Because performance of T. hammondii is not compromised, selective pressure against consumption of X. laevis probably is absent.