A nonorthogonal time-domain full-wave solver of Maxwell's equations was implemented based on the discrete surface integral (DSI) technique. Closed-form expressions were derived for the coefficients used in the time-advancing scheme, in order that the DSI technique could be applied as an explicit generalized finite-difference-time-domain (FDTD) procedure. The FDTD-DSI scheme was employed to investigate the wave-propagation characteristics in multihole waveguide couplers. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 208–213, 1997.