A bifurcation problem for the equation ∆u + λu − αu + + βu − + g(λ, u) = 0 in a bounded domain in Ê N with mixed boundary conditions, given nonnegative functions α, β ∈ L∞ and a small perturbation g is considered. The existence of a global bifurcation between two given simple eigenvalues λ (1) , λ (2) of the Laplacian is proved under some assumptions about the supports of the functions α, β. These assumptions are given by the character of the eigenfunctions of the Laplacian corresponding to λ (1) , λ (2) .