A study of the linguistic interference of nine multilingual immigrants to the Saguenay Peninsula of Quebec province examined three types of interference in their spoken English. They included: (1) interlingual interference from the mother tongue; (2) intralingual intrusion from structures and lexical items from within English in situations and grammatical contexts in which they are inappropriate; and (3) tertiary interference from the language of the community, French. Of the nine immigrants, three had German as their mother tongue, three had Polish, and three had Spanish. A secondary goal of the study was to establish the pedagogical implications emerging from any third language learning difficulties common to all three language groups or unique to each subject. Over a thousand idiosyncratic utterances in English of the nine individuals were analyzed, and errors were placed in the three interference categories. In all cases, interference from French was almost exclusively observable in lexical transfer with little influence on English syntax or morphology. Interlingual interference from the mother tongue was most predominant in the syntax of all subjects' performance in English, although occurring in lexis as well. Intralingual interference was almost the only source of error in morphology. Three principal pedagogical considerations were found: (1) the mother tongue has a strong influence on performance of third language learners, and teacher knowledge of the mother tongue would be helpful; (2) because the second language is an active source of lexical transfer, immigrants to Quebec are apt to transfer items directly from French to English; and (3) error analysis shows that communication can be made adequately despite all errors made, resulting in fossilization of errors and resistance to pedagogical intervention. Tables of errors are appended. (MSE)