After rapid improvement of treatment results in adult acute lymphoblastic leukemia (ALL) from less than 10% to 30-40% in the past decades, more recently stagnation has been observed. In addition, a borderline for further intensification of chemotherapy appears to be reached in adult ALL patients. New, preferably non-chemotherapy, approaches are therefore urgently required. One of those is targeted therapy with monoclonal antibodies (MoAbs). ALL blast cells express a variety of specific antigens which may serve as targets, such as CD19, CD20, CD22, CD33, and CD52. Published results of MoAbs in ALL are reviewed. Most experience is available for anti-CD20 (rituximab) which led to a significant improvement of the outcome in B-cell non-Hodgkin's lymphoma (NHL). In ALL, rituximab is combined with chemotherapy mainly in mature B-ALL and Burkitt's lymphoma and preliminary results are promising. In the future, studies will also be done in B-precursor ALL. Another promising B-cell antibody is anti-CD22. Several CD19 MoAbs were also tested in phase I studies. However, results are not conclusive and these MoAbs are not generally available. Far less experience with MoAb therapy is available for T-ALL, but clinical studies are on the way with anti-CD52 and anti-CD25 in adult T-cell leukemia/lymphoma. Overall, it can be stated that MoAb therapy in ALL is a promising treatment approach. Monotherapy with MoAbs in relapsed ALL occasionally led to responses, but higher effectivity can be expected from a combination with chemotherapy and treatment in the state of minimal residual disease. Well-designed studies and joint efforts are required to explore optimal combinations, timing and dosage of MoAb therapy in ALL.