Sera from patients with primary fibromyalgia (223 sera, 210 women; 13 men) were analyzed, by immunofluorescence microscopy, for the presence of antibodies directed against cell nuclei (ANA), smooth muscle, mitochondria and other tissue antigens present in cryostat sections of rat organs (liver, kidney and stomach). Sera from blood donors (255 sera, 75 women; 180 men) served as a comparative group. The occurrence of serum autoantibodies in patients with fibromyalgia did not differ significantly from the reference group. Our results differ from those of others, who have suggested a relation between fibromyalgia and inflammatory rheumatic diseases.