With the aid of the symbolic calculating language MACSYMA, a program system has been realized for analyzing and designing the nonlinear system equations x=f(x, u), y=h(x, u). The special features of the program are on one hand the examination of controllability and observability of nonlinear systems, and on the other hand the design of nonlinear state feedback systems and state estimators. A rule-based handling of the program helps the user to select and to execute suitable analysis and design procedures. For this purpose, special structures of the nonlinear system equations, e.g. bilinear or canonical forms are recognized by symbolic calculations. Moreover, several heuristic and system theoretic rules are implemented in the MACSYMA program for application of the nonlinear methods. For a numeric evaluation and simulation of the symbolic results, interfaces to the external program systems ACSL and MATLAB are available.