An experiment was conducted to test two predictions entailed by the hypothesis that Japanese morae have constant durations. The first prediction is that a segment’s duration will conform to its moraic status in an utterance; a consonant will be longer when it is syllabic than when it occurs in a GV mora, and phonemically long consonants will have durations that reflect their moraic structure. The second prediction is that segment lengths will vary to compensate for the intrinsic durations of adjacent segments in order to equalize mora lengths. Neither of these predictions was borne out.