Direct intralymphatic administration of radiolabeled monoclonal antibody in targeting antigen-bearing lymphoma cells in regional lymph nodes of patients with cutaneous T-cell lymphoma was evaluated. Seven consecutive patients undergoing staging lymphangiography received intralymphatic infusions of 111In-T101 to evaluate lymph node involvement. This procedure was accomplished without significant complication. The 111In-T101 rapidly distributed throughout the regional lymphatic compartment and passed into the systemic circulation. Tumor-bearing sites in the inguinal-femoral lymph nodes retained from 0.42 to 4.8% of the injected dose of radiolabeled antibody. Three patients were upstaged to Stage IVA based on tumor involvement found after radiolymphoscintigraphy-directed biopsy of groin lymph nodes, selected because of intense radioactivity by gamma camera imaging. Compared with previously reported s.c. antibody administration, there was a marked reduction in the radioactive exposure of normal tissues at the injection sites in the lower extremities. Direct intralymphatic delivery of 111In-T101 appears to be a feasible, efficient method for delivering therapeutic doses of radiolabeled antibody.