This study investigates the relationship of language proficiency to language production and negotiation of meaning that non-native speakers (NNSs) produced in an online task-based language learning (TBLL) environment. Fourteen NNS-NNS dyads collaboratively completed four communicative tasks, using an online TBLL environment specifically designed for this study and a chat tool in WebCT-Vista. Seven dyads were at intermediate-level language proficiency and the remaining seven dyads were at advanced-level language proficiency. Language production was investigated in terms of fluency, accuracy, and complexity including lexical and syntactic complexity, and negotiation of meaning was examined using the ratio of negotiated turns to total turns. The data from the chat-scripts showed that intermediate-level NNSs get involved in more negotiation of meaning than advanced-level NNSs, and advanced-level NNSs produced more accurate language than intermediate-level NNSs. (Contains 5 figures, 5 excerpts, and 5 tables.)