Abstract. We look for solutions E : Ω → R 3 of the problem, where ∇× denotes the curl operator in R 3 . The equation describes the propagation of the time-harmonic electric field ℜ{E(x)e iωt } in a nonlinear isotropic material Ω with λ = −µεω 2 ≤ 0, where µ and ε stand for the permeability and the linear part of the permittivity of the material. The nonlinear term |E| p−2 E with p > 2 is responsible for the nonlinear polarisation of Ω and the boundary conditions are those for Ω surrounded by a perfect conductor. The problem has a variational structure and we deal with the critical value p, for instance, in convex domains Ω or in domains with C
1,1boundary, p = 6 = 2 * is the Sobolev critical exponent and we get the quintic nonlinearity in the equation. We show that there exist a cylindrically symmetric ground state solution and a finite number of cylindrically symmetric bound states depending on λ ≤ 0. We develop a new critical point theory which allows to solve the problem, and which enables us to treat more general anisotropic media as well as other variational problems.MSC 2010: Primary: 35Q60; Secondary: 35J20, 58E05, 35B33, 78A25