Oral administration of 5 mg. of benzene six times weekly to 46 mice that had been injected 24 hours before with the cells of the myeloid chloroleukemia 1394, considerably prolonged the survival of the animals, and in 16 of these mice it seemed to prevent the development of the disease. The spleens of the animals so treated increased in size at a much slower rate than those of the untreated animals, and the leukemic infiltration of the organs was delayed.

Five mg. of benzene given in a similar manner to mice with advanced chloroleukemia likewise prolonged the survival time of the mice and also slowed the rate of increase of the size of the spleens; 25 mg. given five times in a 6 day period to mice with this leukemia brought about a marked reduction in the size of the spleens. Further treatments slowed the rate of enlargement of the spleens and survival was prolonged.

In 8 mice bearing subcutaneous tumors composed of the cells of the chloroleukemia the oral administration of 25 mg. of benzene five times in a 6 day period followed by 5 mg. given six times weekly brought about the disappearance of the local tumors as determined by palpation, but in 6 mice the tumors recurred and killed the animals. Microscopic examination of tumors of mice treated with benzene showed advanced degenerative changes in leukemic cells.

The authors with to thank Miss Pauline Pope, Miss Mary Boon, and Miss Lucille Wolf for their technical assistance.