In this article, centrality is explored as a measure of computer-mediated communication (CMC) in networked learning. Centrality measure is quite common in performing social network analysis (SNA) and in analysing social cohesion, strength of ties and influence in CMC, and computer-supported collaborative learning research. It argues that measuring centrality using SNA is rather misleading, that in fact, it is a relational effect of many things, not just those tied by message threads in online forums. The network data described and analysed were obtained from the students training to be history teachers at the secondary level of schooling in a postgraduate certificate programme in an English university. Blackboard[R] (a commercial virtual learning environment) was used in the course. Online postings in 14 separate forums were considered alongside the perceived relational ties of the teacher trainees in six different communication media (i.e. face-to-face, discussion board, mobile phone, email, land phone, and online chat). This article elucidates that centrality in networked learning is "fluid"--actors (i.e. participants in the online forums) and their relational ties cannot be treated as predictable and fixed and central actors cannot be solely inferred from the total number of online postings and their resulting centrality measure in online forums. (Contains 10 figures.)