Maintenance chemotherapy consisting of weekly oral 6-thioguanine and intramuscular cytosine arabinoside was administered to 24 adult patients with acute non-lymphocytic leukæmia in complete remission. The median duration of complete remission was 16.5 months, with 9 patients (38%) still in their first remission after 18-56 months. 33% of the patients have been in continuous remission for over 2 yr, 21% for over 3 yr, and 12.5% for over 4 yr. Median survival so far is 22.5 months. This maintenance regimen is well tolerated, is easily administered on an outpatient basis, and produces substantial numbers of long-term remissions.