We present TwoTowers, a tool for analyzing functional and performance properties of concurrent systems expressed as terms in the stochastically timed reward process algebra EMPA r . TwoTowers builds on two existing tools, CWBNC and MarCA, that have been retargeted to carry out functional and performance analysis (respectively) of EMPA r system specifications. As an example, we describe the application of TwoTowers to the Lehmann-Rabin randomized distributed algorithm for the dining philosopher problem. Keywords Software tools, process algebras, performance evaluation, Markov chains 1 INTRODUCTION The desirability of taking account of the performance aspects of a system in the early stages of its design has been widely recognized (Yemini et al. 1982, Ferrari 1986, Harvey 1986, Bochmann et al. 1988). Nevertheless, it often happens that a concurrent system is tested for efficiency only after it has been fully designed and tested for functionality. This results in two problems. On the ..