Abstract We conduct a detailed study of the performance effects of irregular communication patterns on the CM-2. We characterize the communication capabilities of the CM-2 under a variety of controlled conditions. In the process of carrying out our performance evaluation, we develop and make extensive use of a parameterized synthetic mesh. In addition we carry out timings with unstructured meshes generated for aerodynamic codes and a set of sparse matrices with banded patterns of nonzeros. This benchmarking suite stresses the communication capabilities of the CM-2 in a range of different ways. Our benchmark results demonstrate that it is possible to make effective use of much of the massive concurrency available in the communication network.