Procedures are presented that are designed to help users efficiently program irregular problems (e.g. unstructured mesh sweeps, sparse matrix codes, adaptive mesh partial dif- ferential equations solvers) on distributed memory machines. These procedures are also designed for use in compilers for distributed memory multiprocessors. The portable CHAOS pro- cedures are designed to support dynamic data distributions and to automatically generate send and receive messsage by capturing communications patterns at runtime. (Also cross-referenced as UMIACS-TR-95-34)