This invention relates to compositions and methods comprising "lymphotoxin-.beta. receptor blocking agents", which block lymphotoxin-.beta. receptor signalling. Lymphotoxin-.beta. receptor blocking agents are useful for treating lymphocyte-mediated immunological diseases, and more particularly, for inhibiting Th1 cell-mediated immune responses. This invention relates to soluble forms of the lymphotoxin-.beta. receptor extracellular domain that act as lymphotoxin-.beta. receptor blocking agents. This invention also relates to the use of antibodies directed against either the lymphotoxin-.beta. receptor or its ligand, surface lymphotoxin, that act as lymphotoxin-.beta. receptor blocking agents. A novel screening method for selecting soluble receptors, antibodies and other agents that block LT-.beta. receptor signalling is provided.