In the present study we examined the role of pitch contours in constraining lexical activation with three priming experiments in Mandarin. Primes based on pitch contours were found to significantly facilitate vocal responses in naming tasks but did not seem to affect lexical processing. Primes containing segments unrelated to the target, but with a tone that matched the target significantly delay responses and, presumably, lexical selection. The delay was found in a shadowing task as well as a lexical decision task. This is the first report of inhibitory lexical effects of tones when prime and target differ in form; it can be understood as a group activation of candidates with the same tone that increases competition with the representation of the target word.