A case study analyzed the babbling and speech production of an infant, aged 20 to 24 months, whose family members spoke Portuguese, English, and French interchangeably. Focus was on vowel production, choice of lexicon, and the relationship between babbling and speech in the interaction of his languages. The child's utterances were recorded in interactions with family together, with each family member individually, with monolingual English-speaking children, and alone in his room. Results indicate a shift from English to French over the 4-month period. The lexicon included 24 words at 20 months and 98 at 24 months, some with representations in more than one language. The primary language in lexical choices shifted from French dominance to French/English balance and finally a predominance of English words. The French vowel system was dominant. Vowel production followed the choice of target words. Vowel correctness changed distinctly over the taping sessions, with monosyllabic target words pronounced increasingly correctly but with vowels in disyllabic words pronounced with decreasing correctness. The findings support neither a separate-system or single-system hypothesis of language acquisition. The sociophonetic environment appears to have been a critical influence. A 32-item bibliography is included. (MSE)