This study of a group of American teenagers living in Mexico uses a series of questionnaires to measure their degree of bilingualism (in English and Spanish) and biculturalism (in American and Mexican culture). The main hypotheses of this investigation were: (1) after five or more years in Mexico, the teenage subjects will be at least functionally bilingual and bicultural, but their competence and performance are expected to be inferior to that of their monolingual and monocultural counterparts in the United States and Mexico; and (2) the English language and American culture will be dominant over the Spanish language and Mexican culture because of reinforcement by family and school, and because of prestige factors involved. The study's methodology included design or research scheme, testing and control groups, field work, and analysis of data. The data was collected through a battery of questionnaires and tests designed to ascertain general background, language and a cultural background, linguistic cultural association, linguistic acceptability, and dialect distinction. Results supported both of the study's hypotheses. The actual questionnaires and tabular statistical results are included in the text. (EJS)