Tandem language learning a configuration involving pairs of learners with complementary target/native languages is an underexploited but potentially very powerful use of computer-mediated communication (CMC) in second-language pedagogy. Tandem offers the benefits of authentic, culturally grounded interaction, while also promoting a pedagogical focus among participants. CMC-based tandem promises, in addition, those benefits believed to accrue from text-based interaction, in particular, promotion of conscious attention to language forms in the course of meaningful communication. This paper presents data from a study based on the spontaneous interactions of tandem partners during a weekly, term-long synchronous exchange based in a MOO (Object-Oriented Multi-User Domain). It begins with an introduction to the concept of tandem language learning. The theoretical background, sketched briefly, is a model of instructed second-language acquisition that emphasizes the role of metalinguistic awareness. The empirical section examines negotiation of meaning, a discourse phenomenon held to bring about metalinguistic focus, and, more specifically, signal form and focus. The study analyzes learner interactions along the parameters of home country (Ireland or Germany), current tandem role (NS or NNS), and utterance language. It is suggested that the behaviors observed in this project have their roots in both the tandem learning setup and the text-based medium.