Lymphadenopathy with splenomegaly and abnormal leukocytes are present in both leukemia and infectious mononucleosis. To the author's knowledge, the hyperuricemia that often accompanies the leukemic states has not been documented in infectious mononucleosis. Uricacid levels from 13 male and eight female patients were obtained during the acute stages of the disease. The mean serum-uric-acid levels of both male and female patients were found to be significantly elevated. The elevations were found to be maximal within the first two weeks of the disease and tended to parallel the presence of abnormal lymphocytosis. Recent studies indicating an increased nucleic-acid synthesis by the abnormal mononuclear leukocytes in infectious mononucleosis suggest a possible mechanism for the hyperuricemia recorded in this report.