The aim of this experimental study is to investigate the production of stressed and unstressed syllables in Brazilian Portuguese (PB) by two hearing-impaired subjects, one with moderate (HI-M) and the other with severe hearing loss (HIS). A normal hearing-subject’s (NH) speech production is taken as reference for the sake of spectrographic analysis. The acoustic parameters investigated were the duration of the speech segments and F1 and F2 frequencies of the vowel /a/ in different stress positions in a controlled phonetic context. Results show differences in the acoustic parameters due to degree of hearing loss of these subjects, suggesting, as expected, less control of prosodic and segmental production. Keywords: hearing impairment, vowels, formant frequencies, duration.