Thirty-three patients with relapsing or refractory multiple myeloma were treated with 6-Thioguanine (6TG) at a dose of 1 g/M2, with therapy given over four hours every three weeks. The major toxicity seen was myelotoxicity; thrombocytopenia was more commonly noted than neutropenia. One patient achieved a PR, two were clinically improved. 6TG in this short infusion schedule proved to be myelotoxic, but demonstrated little activity in previously treated myeloma patients.