In today’s second language classrooms, students are often asked to work in pairs or small groups. Such collaboration can take place face-to-face, but now more often via computer mediated communication. This paper reports on a study which investigated the effect of the medium of communication on the nature of pair interaction. The study involved six pairs of beginner participants in a Chinese class completing seven different tasks. Each task was completed twice, once face to face (FTF), and once via computer mediated communication (CMC). All pair talk was audio recorded, and on-line communication was logged. Using Storch’s (2002) model of patterns of pair interaction, five patterns were identified: collaborative, cooperative, dominant/dominant, dominant/passive and expert/novice. The medium of communication was found to affect the pattern of interaction. In CMC some pairs became more collaborative, or cooperative. The implications of these findings for language teaching, particularly for the use of CMC in language classes, are discussed.