This study reports on a qualitative small-scale exploratory study which examined the factors influencing 32 Iranian pre-service language teachers' participation in online asynchronous text-based discussion forums. By adopting a multiple case study design and analysing data gathered through semi-structured interviews and participants' online postings, it was found that access to computers and the Internet or high speed Internet, group size, quality of messages, level of instructor's involvement, grades, interface qualities, participants' personal characteristics and attitudes toward online interactions, as well as familiarity and experience with online discussions influenced participants' level of participation in online discussions. Based on the findings, recommendations are made to help language teacher educators to encourage effective online communication practices in similar educational settings.