The report is based on 556 cases admitted over a period of 14 mos. The diagnostic criteria for inclusion were more than 10% "leukocytoid" lymphocytes of the total white count unless the heterophile titer was 1:224 or above or gave a positive absorption test. The peak of the epidemic was in the fall. The incidence of the disease between the ages of 18-21 was increased when correlated with the percentage age composition of the army while from the ages of 21-39 it was proportional to their percentage composition. Negroes were more susceptible than whites. There were 112 cases without any clinical manifestations. In the majority of the others, the onset was acute, with chills or chilliness, fever, sore throat, malaise, headache, generalized aches and pains, sweats and anorexia. Throat involvement was present at some time in 73%. A pneumonitis closely resembling atypical pneumonia was present in 2.5%. Palpable glands were present in practically all. The anterior and posterior cervical nodes were most frequently involved. Constipation was the rule. In 12 cases, there was abdominal pain simulating acute appendicitis. The liver was palpable in 17% and jaundice in 6%. The clinical picture and the liver function tests in the latter indicated a diffuse hepatitis accompanied by obstruction of the bile capillaries. The spleen was palpable in 35%.