Three cases are described presenting with progressive contractures in whom the muscles felt firm and `woody' and a clinical diagnosis of myosclerosis was made in each case. A patient and his young sister were shown to be suffering from spinal muscular atrophy with superimposed, excessive proliferative activity of fibroblasts, and in these cases a beneficial effect of penicillamine was demonstrated. The third case with a clinical picture of myosclerosis was found on muscle biopsy to have extensive inflammatory infiltration of the connective tissue, and responded temporarily at least to high doses of corticosteroids. It is emphasized that several different disease entities can give rise to this clinical picture.