We consider the nonlinear equation −∆u = |u| p−1 u−εu in Ω, u = 0 on ∂Ω, where Ω is a smooth bounded domain in R n , n ≥ 4 , ε is a small positive parameter, and p = (n + 2)/(n − 2). We study the existence of sign-changing solutions that concentrate at some points of the domain. We prove that this problem has no solutions with one positive and one negative bubble. Furthermore, for a family of solutions with exactly two positive bubbles and one negative bubble, we prove that the limits of the blow-up points satisfy a certain condition.