Infectious Mononucleosis and Acute LeukemiaTO OUR knowledge, 26 cases1-15 have been reported of the association of infectious mononucleosis and acute leukemia (Table). In seven instances, the former preceded the latter by one to 36 months, in 16 cases the acute leukemia preceded the infectious mononucleosis by one to 45 months, and in three patients both diseases were diagnosed simultaneously. Twenty-one patients were children or teenagers, perhaps accounting for the 20 cases of acute lymphoblastic leukemia. Three patients had acute monocytic leukemia.The possible relationship, if any, between the Epstein-Barr (EB) virus, infectious mononucleosis, and acute leukemia is far from clear. Although the EB virus has been etiologically linked to Burkitt's lymphoma, its relation to acute lymphoblastic leukemia has not been established. It seems rather far-fetched to state that the coincidence of acute monocytic leukemia and infectious mononucleosis in two elderly patients suggests a causal relationship." Although one report" suggests that the EB virus may be able to activate an oncogenic process in a manner similar to that described for murine leukemia, most authors are of the opinion that infectious mononu¬ cleosis is an intercurrent illness that is etiologically