The recombinant CD3 immunotoxin, A-dmDT390-bisFv(UCHT1), composed of the catalytic and translocation domains of diphtheria toxin fused to two single chain Fv fragments of an anti-CD3η monoclonal antibody was administered to five patients with cutaneous T cell lymphoma (CTCL) by eight 15 min intravenous infusions over four days. Side effects were fever, chills, nausea, hypoalbuminemia, transaminasemia and reactivation of EBV and CMV. Half-life of drug was 40 min. Anti-immunotoxin antibodies developed in all patients after two weeks. Two patients had partial remissions lasting 1 and 6+ months. The agent is undergoing further dose escalation and shows promising results in this disease.