Supermon is a flexible set of tools for high speed, scalable cluster monitoring. Node behavior can be monitored much faster than with other commonly used methods (e.g., rstatd). In addition, Supermon uses a data protocol based on symbolic expressions (S-expressions) at al l levels of Supermon, from individual nodes to entire clusters. This contributes to Supermon's scalability and al lows it to function in a heterogeneous environment. This paper presents the Supermon architecture and discuss initial performance measurements on a cluster of heterogeneous Alpha-processor based nodes.