In a series of attempts to transmit a virus from patients in the acute stages of rheumatic fever, twenty-seven rabbits and fourteen guinea pigs were inoculated with one of the following materials: whole blood, serum, joint fluid, pleural fluid, throat washings, suspensions of tonsil tissue. Subsequent transfer inoculations from animal to animal brought the total number of animals employed in the experiments to 67 rabbits and 40 guinea pigs. Only two animals developed an acute non-bacterial arthritis. No other evidence of successful transmission of the disease was obtained. In about one-half of the rabbits and two-thirds of the guinea pigs myocardial lesions were encountered which consisted of interstitial accumulations of lymphocytes and endothelial cells. Similar lesions were found in control animals.