Some coupled nonlinear equations are considered for studying traveling-wave solutions. By introducing a stream function ψ it is shown that if one of the solutions is of the form v≡v(x - ct), the other also must be of the form u≡u (x - ct). In addition, the possibility of including cubic nonlinear terms has been considered and such a system, assuming that the solutions are of the traveling-wave type, has been solved. © 1986 American Institute of Physics.