A study of vowel substitution in Finnish learners of English as a second language looked at the quantitative characteristics of qualitatively similar vowels under different tempo conditions. Specifically, it compared the effects of rate of speech and vowel duration on the eleven stressed monophthongal English vowels and their Finnish counterparts. Tape recordings of instances of the vowels were translated onto an oscillograph, and trace intervals representing the object vowels were segmented, measured, and statistically analyzed. Marked interlingual differences were found, with English relying more on qualitative vowel features and Finnish relying more on quantitative features for distinguishing between phonemes. In Finnish there appears to be systematic pressure for homogeneity within phonemic length categories that is strong enough to level out inherent durational differences between qualitatively different vowels. The duration of English vowels appears to be less affected by changes in speech rate. The report stresses that the results are statistical and not linguistically-based, and that further linguistic and perception testing is necessary to assess the linguistic significance of the findings. (MSE)