This study is an investigation into the nature of the vowel phonemes of Bahasa Indonesia in monosyllabic words, under primary stress, and consisting of a consonant followed by vowel followed by a consonant. Bahasa Indonesia is the national language of the Republic of Indonesia. All of the material in the literature relating to the vowel quality of this language is highly impressionistic. Some of the descriptions are comparisons with vowels in various modern Indo-European languages rather than scientific descriptions of strictly Indonesian vowel quality.