A study of the acquisition of Turkish and German by immigrant children in West Germany addressed three issues: (1) the role of cognitive development and age of learning in the process of language acquisition, (2) the role of transfer between languages, and (3) the effects of greater or lesser contact with native speakers of the two languages being acquired. The examination focused on the nominal reference system characterized by plurifunctionality and syncretism. Data were drawn from two cross-sectional studies of bilingual immigrant children in West Berlin in which the sociopolitical setting is considered along with the psycholinguistic investigation. The age groups were 8-15 years and 5-12 years. Monolingual German and Turkish control groups were used in the second study. The children's production of definite and indefinite markers during lengthy interviews using a variety of psycho- and sociolinguistic methodologies was analyzed. The data suggest that, while the individual learner's approach to plurifunctional items is systematic, individual interlanguage systems differ from each other. Further research into the points at which the various functions of plurifunctional items become the focus for individual learners is recommended. (MSE)