The purpose of the study was to investigate the sound commonly known as "final /r/" or "postvocalic /r/", and to determine its structure and behavior in various contexts of stress and position within the phonetic phrase. Interaction and assimilation of the "postvocalic /r/" with the vowels /I/ and /U/ were of chief concern, as the hypothesis was that the "postvocalic /r/" did not actually exist following (at least) those two vowels; that, rather, when the /r/ was preceded by /I/ or /U/ in the same syllable, the two combined to form one diphthongal element, for which the writer used the symbols /E/ and / f/, depicting the /r/ coloring and assimilation of the vowels.The study was designed to explore several facets of what actually happened, in terms of phonetic and acoustic structure, when /r/ followed the two aforementioned vowels in the same syllable. At least three possibilities were realized at the outset of the investigation: 1) that, despite their adjacency, the sounds remained as two separate sounds and two separate syllables, 2) that the two merged as one sound lengthened to cover two syllables or beats, and 3) that the result of the assimilation was one sound and one beat. Thus, a large part of the problem was semantic in nature, for the question was, "When /r/ followed a vowel of the same syllable, was the resultant sound unit called a vowel, a diphthong, or something entirely new?"Due to the question of structure, the writer concerned herself with the use of phonetic symbols in discussion of the problem. The new symbols /-./ and /-S / originated with Dr. Alan W. Huckleberry, Chairman of the Department of Speech at Ball State University in Muncie, Indiana. Though the symbols were logical phonetically, following the same principle as the use of the "hook" on the /a/ and the /3 / (25, p. xix) they were not believed applicable in all contexts of stress and position within the phrase. Therefore, the writer included the possibility of the schwar, or "hooked schwa" /-'/ as functioning in cases of extreme diphthongization of the test units. Spectrographic analysis was required to investigate and more clearly determine the proper use of each symbol.Significance of the study was based on the belief that added research could be of value to phoneticians and their use of the IPA (International Phonetic Alphabet) and could aid in lessening some of the present confusion concerning the /r/ phoneme.