In an attempt to test the hypothesis that stuttering is the result of discoordination between phonation and articulation, 10 adult stutterers and 10 adult nonstutterers were asked to produce prolonged versions of /z/ and /s/ sounds, as quickly as possible, in response to tone stimuli. It was hypothesized that stutterers would exhibit significantly longer reaction time (RT) for the /z/, a voiced sound, than would a similar group of nonstutterers, whereas the two groups would not differ in RT for the /s/ sound, the unvoiced counterpart of /z/. The results showed that stutterers as a group did not differ from nonstutterers in RT for either the /z/ of the /s/ sound. However, it was found that severe stutterers exhibited significantly longer RTs for the /z/ sound than did mild stutterers. There were no differences between severe and mild stutterers in RT for the /s/ sound.