An approach to robustness analysis in discrete-time MIMO control systems is developed by using the closed-loop characteristic equation in the presence of gain or phase perturbations. Genetic algorithms are also proposed as the search algorithm for determining the smallest destabilizing perturbations in the form of MIMO gain and phase margins. This technique is computationally more burdensome than the calculus-based technique. However, it can deal with digital control systems, which include time delays, in the exact manner.