Seven patients with refractory multiple myeloma (readily evaluable for response) were treated in a Phase II trial with poly(I,C)-LC using a 3 times per week intravenous schedule. Serial immunologic testing included assessment of natural killer (NK) cell activity, antibody-dependent cytotoxicity, delayed hypersensitivity, and in vitro mitogen responses. One patient had a partial response (PR) of 6-month duration, and 3 other patients had objective responses (less than PR). Significant interferon induction occurred, but levels dropped substantially with serial dosing. Major toxicity included hypertension, hypotension, fever, and myelosuppression. The demonstration of modulation of myeloma progression in this refractory population was encouraging.