The problems of measuring the performance of a highly parallel multiple processor system, such as the 4096 element ICL Distributed Array Processor are presented in relation to the conventional methods used for serial processors; this is preceded by a brief description of the DAP hardware in order to. provide a framework for the discussion, together with some of the resulting implications for algorithm design. The importance of choosing algorithms for parallel computation in such a way as to make the best use of the parallelism of the hardware for the problem to be solved is discussed, and examples are given of parallel and hybrid algorithms?in the latter a mixture of serial and parallel techniques are used. A method of comparison of performance at the problem solving level is presented, which is illustrated by results obtained by DAP users studying problems which arise in a wide range of application areas.