THE DIFFICULTY encountered in differentiating acute disseminated lupus erythematosus from dermatomyositis prompted us to evaluate muscle biopsies on a series of patients with these diseases, and, because Hargraves found a heretofore undescribed cell in bone marrow preparations from patients with acute disseminated lupus erythematosus, we added a search for such cells to our investigations. The following communication is an effort to compare and correlate the observations made during such searches on 27 patients, 8 of whom had dermatomyositis and 19 of whom had lupus erythematosus (11, acute disseminated; 7, subacute, and 1, chronic). There are a large number of diseases which are similar and often confused with the two diseases under discussion. The list is long and emphasizes why any positive aids in diagnosis should be carefully appraised. Poikiloderma atrophicans vasculare,1 diffuse scleroderma,2 scleredema adultorum,3 trichinosis, polyarteritis nodosa, glomerulonephritis,4 myasthenia gravis,5 pellagra,