question: A new disease of rabbits is described. Following an acute febrile course, animals die or recover by the 11th day postinoculation. The characteristic pathologic finding is multifocal myocardial degeneration and necrosis. The disease can be transmitted by various routes with tissue filtrates or with infectious sera diluted to 10(-6) and passed through 0.1 micron filters. Virus particles with morphologic features characteristic of a coronavirus are present in infectious but not in normal rabbit serums. The antigen(s) in the infectious serums cross-reacts with the 229E and the OC43 strains of human coronavirus. Antigen cross-reacting with the 229E virus is detectable by immunofluorescent staining in frozen sections of heart tissue from sick but not from healthy animals. Animals surviving infection seroconvert to coronavirus specificity, as demonstrated by the presence in convalescent serums of antibody capable of reacting with the 339E virus. Susceptibility to infection has not been demonstrated in mice, hamsters, or guinea pigs, and the virus was not adapted for growth in tissue culture. It is uncertain whether the agent is a natural pathogen of rabbits or a coronavirus contaminant from another species, possibly human. The name rabbit infectious cardiomyopathy is suggested for this disease.