Disclosed are compositions and methods comprising combinations of anti-CD74 antibodies with a therapeutic agent that is attached to the anti-CD74 antibody or separately administered. Preferably, the therapeutic agent is an antibody that binds to an antigen different from CD74, such as CD19, CD20, CD21, CD22, CD23, CD37, CD40, CD40L, CD52, CD80, IL-6, CXCR4 or HLA-DR. However, the therapeutic agent may be an immunomodulator, a cytokine, a toxin or other known therapeutic agent. Preferably, the anti-CD74 antibody is part of a DNL complex. More preferably, combination therapy with the anti-CD74 antibody and therapeutic agent is more effective than antibody alone, therapeutic agent alone, or the combination of unconjugated anti-CD74 antibody and therapeutic agent. Administration of combination induces apoptosis of target cells in diseases in which CD74 is overexpressed, such as solid tumors, B-cell lymphomas or leukemias, autoimmune disease, immune dysfunction disease or diabetes.