The phonological switching processes of 16 bilingual (Spanish-English) adults were observed to provide phonological evidence for the coordinate/compound theory of bilingualism. Each subject was categorized as a coordinate or compound based on responses to a questionnaire. Subjects were recorded reading a mixed list of Spanish and English words. The results were distinctive for both the coordinate and compound groups. Speculations were made concerning possible phonological models for both bilingual groups. An explanation of the test results is based on the operation of the proposed coordinate and compound phonology systems. Implications for further related research are mentioned following a discussion of the results. This study has demonstrated that, in this instance, Spanish and English bilinguals store their Spanish and English phonologies as either one combined system or as two independent systems. (Author/NCR)