A study of the process of bilingualization of second-generation immigrants to Catalonia, a region of Spain, is described and summarized. The study looks at the interrelationships between (1) linguistic context, all sources of messages in natural speech; (2) linguistic behavior, the real communicative use the individual makes of his expressive faculties in the language; and (3) linguistic competence, the combination of knowledge and capacity allowing the individual to understand and utter messages in the language. These variables are examined as they relate to the acquisition of Catalan by Castilian-speaking immigrants' children. The report begins with a general geographic and demographic background and a description of the study's design. The second chapter presents information on the demography and the three linguistic variables examined in the town under study. The third and fourth chapters present analyses of the relationships between the three variables. The fifth chapter outlines the study's conclusions and observations. A bibliography, the data-collection instruments, notes on oral and written responses to the tests used, and extensive statistical tables are appended. (MSE)