A study investigated the role of bilingualism (Basque/Spanish) and motivation in third (English) language acquisition in Spain's Basque country. Subjects were 321 secondary school students in two programs, one with instruction primarily in Spanish and one with instruction primarily in Basque. The following independent variables were analyzed in the subjects: bilingualism (early or late); competence in Basque; monolingual versus bilingual mother; principal language of instruction; general intelligence; attitude toward English; effort made to learn English relative to other subjects; visits to English-speaking countries; and English language instruction outside school. Dependent variables that were examined include achievement in the four language skills (listening, speaking, reading, writing), vocabulary, and grammar. Data were gathered by questionnaire, written tests of English, and interviews in English. Results indicate that: bilinguals performed better in English than monolinguals; highly motivated students performed best; and there were complex interaction effects of bilingualism, motivation, family bilingualism, Basque as the primary language of instruction, and intelligence on English achievement. Contains 32 references. Results of data analyses are appended. (MSE)