The present invention relates to humanized immunoglobulins having binding specificity for α4β7 integrin, comprising an antigen binding region of nonhuman origin (e.g., rodent) and at least a portion of an immunoglobulin of human origin (e.g., a human framework region, a human constant region). In one embodiment, the humanized immunoglobulin can compete with murine Act-1 for binding to human α4β7 integrin. In a preferred embodiment, the antigen binding region of the humanized immunoglobulin comprises each of the complementarity determining regions of the light and heavy chains of the murine Act-1 antibody.