This study compares two diphthongs ([ea], [oa]) and two glide-vowel sequences ([ja], [wa]) in Romanian. The diphthongs and the sequences are auditorily very similar, but they differ in their phonological patterning. An integrated production and perception experiment is conducted in search of perceptual and acoustic evidence for the different phonological representations proposed for the diphthongs and the sequences. Four acoustic parameters of the diphthongs and sequences are measured and compared in a production study. In addition, a perception experiment tests native speakers' ability to correctly identify the two types of vocalic sequences. The results support the different representations proposed for [ea] vs. [ja], but not necessarily for [oa] vs. [wa]. This asymmetry is interpreted in the context of language-specific frequency differences, and of contrast maintenance. The study shows that detailed phonetic description is needed for a complete understanding of the phonological facts.