Monoclonal antibody 9.2.27 (mAb 9.2.27) directed to a chondroitin sulfate proteoglycan on human melanoma cells was able to suppress tumor growth in athymic (nu/nu) mice more effectively when bound with polyethylene glycol to murine effector cells than when injected alone. These "armed" effector cells also proved more effective than the monoclonal antibody in eliciting antibody-dependent cellular cytotoxicity against human melanoma target cells in vitro.