This study tests whether Farsi vowels are contrastive with respective to length. Farsi has a six-vowel system with three lax vowels and three tense vowels. Both traditional grammarians and modern linguists believe that Farsi tense vowels are longer than lax vowels, and that there are no vowel pairs that contrast only in length. However, it has been suggested that Farsi exhibits compensatory lengthening, which is triggered by the deletion of glottal consonants in coda position in informal speech (Darzi, 1991). As a result, minimal pairs such as [tar] and [tarh] should contrast only with respect to vowel length. A corpus of 90 words of the form CVC, CVCG, CVGC, and CVCC (where V=a vowel and G=a glottal consonant) was recorded, and durations of vowels in different contexts were measured and compared. Preliminary results show that lax vowel durations fall into three groups with CVCC longer than CVCG/CVGC, and the latter longer than CVC. It remains to be seen whether CVCG/CVGC words show compensatory lengthening when the glottal consonant is deleted.