Antinuclear and anticytoplasmic antibodies were detected, using 4 methods, in 96% of the sera (23/24) from 24 dermato- or polymyositis patients, who were followed in the Rheumatology Department. Immunofluorescent (IF) labeling of Hep-2 cell smears was more sensitive than IF staining of liver sections (72 vs 67%), and the patterns observed were in agreement 20/24 times. Gelose precipitation is even less sensitive (29%), but enables a characterization of the antigens recognized: 3 anti-RNP, 3 anti-J01, 1 anti-PMScl, 1 anti-SSB and 1 anti-Ro; the latter two specificities were associated with a sicca syndrome. Western-blotting was the most informative method because it was highly sensitive (79%) and identified the principle antigen-antibody systems: anti-U1-RNP (33%) and anti-Scl70 (33%), both associated with myositis with an overlap syndrome (p less than 0.02); anti-J01 (25%) associated with various forms of myositis; and, more rarely, anti-SSB and anti-Ro (both 4%) when a sicca syndrome was present. Finally, non-identified specificities were observed in 37% of the cases.