A retrospective study of 136 bone marrow aspirates was undertaken before treatment to evaluate the importance of bone marrow eosinophilia in Hodgkin's disease. This occurred in 28 patients (21%) but did not correlate with age, sex, B symptoms, histopathological type or peripheral blood count. It also had no effect on survival. Bone marrow eosinophilia, therefore, seems to represent a common but non-specific reaction to Hodgkin's disease.