Thirteen patients having stage II or III mycosis fungoides were treated with azaribine, a new anti-metabolic agent. Eleven of 12 patients adequately treated responded. Seven patients experienced complete clinical remissions that lasted up to 176 weeks. The amount of drug toxicity observed with azaribine, when contrasted with those experienced with other less effective cytotoxic agents, was considered to be minimal in severity. Spontaneously reversible toxic effects to the central nervous system occurred during the first two weeks of therapy in five patients. No detectable abnormalities occurred in liver or kidney function. It is concluded that azaribine, in our experience with this group of 13 patents was more effective and less toxic than other previously described chemotherapeutic agents. The therapeutic results recorded here compare favorably with those reported with use of various forms of radiotherapy.