1. 6-Chloropurine, an analogue of 6-mercaptopurine, has been shown to produce complete remissions in three and partial remissions in eight of 30 adults with acute leukemia. No beneficial effects were obtained in four additional patients known to be resistant to 6-mercaptopurine.
2. Three of four patients with chronic granulocytic leukemia responded to 6-chloropurine.
3. Slight objective improvement was noted in patients with lymphomas but only at the point of hematologic toxicity.
4. A high incidence of jaundice was noted, but it is difficult to relate this definitely to the therapy.
5. While 6-chloropurine appears to be slightly superior to 6-mercaptopurine in acute leukemia in adults, the pattern of response would indicate that these agents have a similar mechanism and range of therapeutic activity.