Unstressed vowels in Russian are reduced in both duration and quality, but these two manifestations of vowel reduction do not have to be observed simultaneously. In order to investigate this question, we analysed the reduction pattern of words in such contexts where lengthening is induced by prosodic factors: prominence and pre-boundary lengthening. The study is based on a large corpus of read speech. The following results were obtained: (1) as expected, both contexts increase vowel duration; (2) under prosodic prominence vowels undergo less qualitative reduction, while pre-boundary lengthening has no effect on qualitative reduction; (3) additionally, it was shown that prominence mainly affects the pretonic part of the word, while pre-boundary lengthening-the post-tonic part. Thus, an increase in vowel duration does not always cause a decrease in qualitative reduction, which may serve as evidence against the idea that qualitative reduction is caused by quantitative reduction. Additionally, these results may serve as an argument for the idea that the two processes-vowel reduction and temporal organization of utterance-are autonomous.