Abstract: Fifteen muscle biopsy specimens of eosinophilic fasciitis and ninety-four postmorten muscle specimens from patients dying of non-muscular disease were studied under the light microscope. Out of ninety-four pieces,twenty-two pieces practically showed no deep fascia and seventy-two pieces showed only a single dense bundle of collagen with no distinction between deep fascia and epimysium. The fifteen specimens of eosinophilic fasciitis showed thickening and inflammatory infiltration of varying degrees of the deep fascia,epimysium,permysium and endomysium and involvment of muscle,so a conclusion was reached that the pathologic change of eosinophilic fasciitis not only lay in the deep fascia but also in the mysiums and muscles. A comparative study of fifteen biopsy specimens of polymyositis with those of eosinophilic fasciitis revealed only quantitative differences in the muscle,mysiums,inflammatory infliltration and eosinophilia between the two diseases,therefore,a suggestion was made that those two were probably two extremes of a broad spectrum.