In this study lexical stress of homographs uttered by speakers with three different levels of English, namely native Americans, Taiwanese students specializing in English and students with basic knowledge of English, is investigated. The acoustic properties of duration, fundamental frequency and intensity are studied. A new measure is proposed based on the ratio of successive vowels that is insensitive to speaker and speed variations. The results show that the degree to which duration and fundamental frequencies are varied in successive vowels is related to the English level of the speaker. Intensity was not found to be a significant cue.