There is a lively debate in the phonetic literature as to whether phonological neutralization is phonetically complete. Almost all phonetic studies of neutralization have focused on word-final devoicing, with findings supporting either complete or incomplete neutralization. The present study investigated a different type of neutralization, namely that of manner of articulation. Korean has a rule of manner neutralization whereby underlying /s/ surfaces as [t] in syllable-final position. Underlying /t,th/ will also surface as [t], resulting in minimal pairs that differ in terms of the manner of the final consonant in the underlying but not in the surface representation. Making use of the fact that vowels preceding fricatives are longer than when preceding oral stops, we examined vowel and closure durations to determine if the speech signal contained any cues to the underlying manner distinction. Data from four speakers suggest that this neutralization of manner is phonetically complete. Implications of these results for the relation between phonological and phonetic representations will be discussed.