A solid phase fluorometric assay of high sensitivity and specificity for detection of antimyosin antibodies is described. The method consists of 4 basic steps: (1) coating the carrier stiQ with myosin; (2) incubation of the stiQ in the test serum; (3) labeling of the bound antibodies by FITC-anti-immunoglobulin antibodies; and, (4) quantitation of the bound antibodies in a fluorometer (FIAXTM). Using a purified myosin preparation as antigen, the assay was tested in experimental myocarditis of rabbits injected with cardiac proteins. Reproducibility was excellent, standard deviation of intra-assay variance being 7.86%, and inter-assay variance 9.45%. When compared with immunodiffusion, a complement fixation test with myosin and indirect immunofluorescence, the assay described proved superior since it allows simple monitoring of serum concentrations of antimyosin antibodies.