The results are presented of serological tests by the neutralization method for 
antigens of Coxsackie B group, and by the haemagglutination inhibition method 
for three types of parainfluenza and sporadic influenza virus in 529 patients 
with myocarditis. In 7 cases the virus was isolated from stools. Virus aetiology 
of the disease was confirmed in 23.4% of cases, on average. Raised levels of 
antibodies to Coxsackie B antigens were found more frequently than the levels of 
antibodies to parainfluenza viruses. Seroconversion was more frequent in 
infections by parainfluenza type 3 than type 2. During an influenza epidemic in 
5 cases raised levels of antibodies to the epidemic-causing strain were 
observed.