111Indium-monoclonal antimyosin scans were carried out in 21 patients with suspected myocarditis, confirmed by reduced ejection volume, pericardial effusion and clinical follow up in 12 patients. Coronary heart disease was excluded angiographically in all cases. Quantitative evaluation of myocardial 111In-antimyosin accumulation 48 hours after injection showed a pathological uptake in 10/12 patients with increased heart/lung ratios (Q48 greater than 1.58). Ratios were also elevated in 2 patients with cardiomyopathy, 2 suffering from vasculitis and 1 with dermatomyositis. Four patients without proven cardiac disease had normal ratios (Q48 less than or equal to 1.58). Examination after 24 hours was of limited value, depending on the residual blood pool activity. Visual analysis of the scans showed a high interobserver variation despite a positive correlation with quantitative analysis (48 h p.i.: r = 0.72; p less than 0.001), and is not recommended. The results show the value of the 111In-antimyosin scan as a screening method prior to myocardial biopsy. However, scintigraphy cannot definitely elucidate the cause of myocardial damage. Therefore, myocardial biopsy is still recommended after positive antimyosin scans.