Acoustic duration is subject to modification from multiple sources, for example, utterance position [13] and predictability such as occurrence frequency at word and syllable levels [e.g., 1, 2, 3]. A study of German radio corpus data showed that these two sources interact to modify syllable duration. Other studies have found that the predictability effect can percolate downstream to the segmental level, and that this downstream effect is sensitive to phonemic contrasts [8]. However, [5] showed that utterance-final lengthening is uniformly applied to tense and lax vowels in German. This then raises some questions as to whether the effects of the two sources of durational variation are uniformly applied or sensitive to phonemic identity. The current study focused on the duration of tense and lax vowels in the stressed syllable of monosyllabic and disyllabic words in utterance-medial and utterance-final positions. Twenty German speakers participated in a question-answer elicitation task. A preliminary analysis of seven speakers showed effects of utterance position and word frequency, as well as interactions with vowel type, suggesting a non-uniform application of durational adjustments contingent on phonemic vowel identity. Interestingly, the frequency effect affects the duration of lax vowels, but utterance position affects the duration of tense vowels