Good profiling is a major issue in extracting performance from parallel programs. We report on a novel synthesis of sequential cost-centre profiling and state-of-the-art parallel simulation for the pure functional language Haskell that promises to provide detailed and accurate information about parallel Haskell programs. Exploiting simulation also improves the quality of sequential cost centre profiling, though at a significant performance overhead. 1 Introduction It has become something of a commonplace for us to complain bitterly of the difficulty of understanding the behaviour of parallel functional programs in the presence of lazy evaluation. In order to help overcome this, we have designed a suite of visual profiling and simulation tools, originally aimed specifically at research into granularity issues, but now also aimed at general parallel program development. Unfortunately, it is still a frequent occurrence for some member of our team to be asked to explain the behaviou...