An overall study, accompanied by some statistics, is presented of delayed bone marrow injuries caused by drugs, such as chloramphenicol, phenylbutazone, oxyphenbutazone, gold salts, sulphamides and diphenylhydantoin. Unanimous agreement as to the aetiological interpretation of isolated cases, the seriousness of marrow damage, and the results obtained by treatment can be observed in various countries. The available epidemiological data are incomplete, though they point to a parallel between the appearance of panmyelopathy after chloramphenicol and the consumption of this drug. First noted in the U.S., this relationship later became apparent in several European countries and eventually in West Germany. Frequencies range from 1 per 6,000 to 1 per 36,000 subjects treated in California, Hamburg and Sweden.