A study explored the relevance of acculturation theory to language fossilization in the advanced stages of second language learning. Case studies of two native Japanese speakers with long experience living in an English-speaking environment are examined. First, the model of acculturation is outlined: it proposes that socio-psychological factors, particularly social and psychological distance, are central to second language learning success and draws a parallel with the development of pidgins and creoles in language contact situations. Second, the research methodology is described and the two subjects are introduced, focusing on their language use patterns and social-psychological profiles. The third section reports results of several English usage analyses (morphemes, negatives and interrogatives, complex syntactic structures, lexis and comprehension, pronunciation) and social-psychological analyses (social distance, status, size, attitudes, cultural congruence, integration patterns, cohesion, enclosure, relations with the expatriate community, psychological distance). It is concluded that acculturation theory does not account for two important factors, language aptitude and language needs, or for fossilization, and that a broader approach is needed. (MSE)