This paper will describe an ESP approach to the design and implementation of computer-mediated communication (CMC) tasks for computer science students at Universiti Teknologi Malaysia, and discuss the effectiveness of the chat feature of Windows NetMeeting as a tool for developing specified language skills. CMC tasks were set within a programme of sustained-content language instruction (SCLI), a variation on the content-based instruction approach. Various studies have confirmed the potential of SCLI as a means of familiarising language learners with academic genres and the language skills expected of them in the content classroom. To date, however, there has been little or no research into the use of CMC within SCLI. We found that students who followed a programme of SCLI using CMC ESP tasks made significant improvements in their oral communication skills, and also achieved higher scores than their peers in a computer science project undertaken in the semester following the treatment. (Contains 8 tables and 1 figure.)