This study examines the occurrence of transfer in the simultaneous acquisition of French and Hebrew by 57 native English-speaking children in a primary grades French/Hebrew immersion program in Montreal. The study focuses on three issues: (1) whether transfer of genetically related first and second languages differs quantitatively and qualitatively from transfer of non-related languages, (2) the characteristics that underlie grammatical and lexical transfer, and (3) the extent of transfer between two second languages being learned simultaneously. The children were administered an oral production test using two techniques, a short interview and a picture-based test. Errors in French and Hebrew were classified as interlingual, intralingual, and ambiguous. The results indicate similarities in the way transfer operates in the two languages as well as differences in performance. Certain types of syntax and lexical errors occurred less frequently in Hebrew than in French, possibly because French is genetically related to English. Lexical transfer is more likely to occur than grammatical transfer, and lexical transfer diminishes more rapidly. Grammatical errors were produced systematically by most learners, possibly because the production of grammatical structures is less influenced by communicative strategies than the production of lexical items. (AMH)