Auditory-motor formant tracking, or the vocal reproduction of formant patterns, is one aspect of speech imitation skill. The study reported here assessed the ability of four adult speakers to imitate synthesized vocalic stimuli. These stimuli took the form of two steady-state segments joined by a transitional segment. The first steady-state segment corresponded to one of eight American English vowels, and the second, to one of 14 vowels that were not expected to have a prominent phonemic identity in the language. Spectrographic analyses of the imitative responses allowed comparisons of the formant structure for the synthesized stimuli and the corresponding human reproductions. Analyses of the spectrograms revealed that the directions of movement for the first two formants were almost always reproduced accurately, but the extent of movement frequently was overshot. These responses were judged to be consistent with a contrast effect in speech perception, a phenomenon previously discovered in experiments on vowel identification. The variability of formant reproduction for a given vowel was predicted at least roughly by the ambiguity of the stimulus in a preliminary identification experiment. These results suggest that the responses in an imitation task are intermediate in dimensionality to the responses in discrimination and identification tasks.