Let G be a balanced bipartite graph with partite sets X and Y, which has a perfect matching, and let x is an element of X and y is an element of Y. Let k be a positive integer. Then we prove that if G has k internally disjoint alternating paths between x and y with respect to some perfect matching, then G has k internally disjoint alternating paths between x and y with respect to every perfect matching. (C) 2004 Elsevier B.V. All rights reserved.