Madurese, an Austronesian language of Indonesia, shows a systematic interaction of consonants and vowels, whereby the voicing or aspiration of a preceding stop conditions the height of the following vowel. In this talk, I investigate both the phonological and phonetic properties of the consonants and vowels in Madurese in order to better understand this unusual pattern of consonant phonation - vowel quality interaction. Two possible phonological interpretations are presented, based on the phonological evidence and acoustic evidence (vowel quality, duration, and pitch) which suggests a "register" system, similar to phenomena seen in the Mon Khmer languages.