In this paper, we present an approach to the solution of the Hamilton-Jacobi-Isaacs equation (HJIE) arising in the H-infinity control problem for nonlinear systems. We show that the HJIE can be solved analogously to a scalar quadratic equation with some additional side conditions, and present a computational procedure for determining symmetric solutions. Examples are given for second-order affine nonlinear systems to illustrate the procedure, and the method can be extended to higher-order systems. (C) 2003 Elsevier Science Ltd. All rights reserved.