In order to study the current clinical status of viral and idiopathic myocarditis in Japan, we conducted a questionnaire survey and collected data for 218 cases from 62 institutions. The diagnosis was based on clinical and laboratory findings alone in 45% of the cases, and it included endomyocardial biopsy in 24% and autopsy in 9% of the patients. Endomyocardial biopsies were available in 40% of the patients; definite cellular infiltrations were identified in half the cases. Regardless of the biopsy findings or availability of biopsy, males predominated in the patient population; the mean age range was 30-39 years for both sexes. Cardiac symptoms and signs were common in addition to "common cold" symptoms; ECG abnormalities, leukocytosis, accelerated erythrocyte sedimentation rate, positive CRP, and increased cardiac enzyme levels were also very common in the acute phase of the disease. Serologic tests for virus titers, performed in 80% of the cases, were positive in 21%. There was no apparent correlation between serologic results and endomyocardial biopsy findings. In this survey, complete recovery occurred in 43%, cure with sequelae in 40%, recurrences in 3%, and death in 13% of the total patient population.