In a recent letter, a new implementation of the complementary operators method (COM) was introduced for 2-D radiation problems. Referred to as the concurrent complementary operators method (C-COM), this new implementation achieved a level of accuracy and efficiency that surpassed that achieved earlier by the classical two solution implementation of COM. This letter extends the application of the C-COM to treat 3-D radiation problems. Numerical results using the finite-difference time-domain method (FDTD) for two representative experiments are presented to demonstrate the effectiveness of this new technique. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 17: 244–247, 1998.