Lymphatic leukemia induced in Wistar rats by the gastric instillation of methylcholanthrene, was transferred to 40-day-old animals of our random bred Wistar colony with only indifferent success. When transfers were made to animals not older than 7 days, these were successful in 100% of the animals. Transfer of the leukemia was also made uniformly to equally young animals of the Sherman and Long-Evans strains. The intraperitoneal injection of leukemic spleen cells was used in these experiments.