We discuss the existence of solutions to the following nonlinear problem involving two critical Sobolev exponentswhere β 0, Q is continuous on ∂Ω, p ∈ H 1 (Ω) is continuous and positive inΩ and f is a lower-order perturbation of |u| 2 * −1 with f (x, 0) = 0.Keywords: Sobolev critical exponent, the trace embedding, variational problem, critical nonlinearity in the boundary, Palais-Smale condition, the mean curvature