In discussing recent progress in the study of the leukemias it proves difficult to point to essentially new developments on the clinical side. These relatively rare diseases are observed for the most part in isolated instances in general hospital services, where opportunity is lacking to make comparisons of large numbers of cases. I believe that the scope of the leukemic processes has not therefore been fully delineated, and that we are still in that stage in the study of these diseases in which profit may be derived from further clinical observations, descriptive reports, and speculation as to relationships and interrelationships. For that reason I have chosen the above title and shall devote this paper to a report of selected cases illustrating different aspects of the course and treatment of leukemia. Duration One remarkable feature of leukemia is the great variation in duration of its course. It may be a fulminating catastrophe or an extremely prolonged, relatively benign affliction. Occasionally myelocytic leukemia will run a course of ten years or longer, but a long course seems somewhat more common in lymphocytic leukemia. The following case furnishes an example of chronic lymphocytic leukemia of fairly long duration.