A case is reported of a young man with acute hemolytic anemia and hemoglobinuria who presented: an initial blood picture consistent with infectious mononucleosis, associated with a heterophile agglutination test positive in high dilution; auto-hemagglutinins, active in the cold, at room temperature and at 37 Centigrade; a hemolysin active at 37 C. after chilling, requiring the presence of a thermolabile component of serum for hemolysis; a positive Donath-Landsteiner test but no evidence of syphilis. In addition there was clubbing of the digits with certain other roentgenologic changes in the bones; absence of any other etiologic factors known to be concerned with such anemia; uneventful improvement under massive transfusion therapy, with apparent recovery from his hematologic disorder when studied two years later.

ACKNOWLEDGMENT Our thanks are due to Dr. Maxwell Finland and Dr. Philip F. Wagley for suggestions in preparing this report. We are especially indebted to Dr. T. Hale Ham for his patient and critical advice and encouragement.