Antibodies against very low-density lipoproteins and low-density lipoproteins (aLA) were found in 26 of 69 (38%) patients with active rheumatoid arthritis (RA) but not in any control subjects (ie, 40 patients with psoriatic arthritis, 21 patients with osteoarthritis, and 65 healthy blood donors). In 21 RA patients (30%), lipoproteins were found in the dissociated components of circulating immune complexes. RA patients with aLA had significantly decreased cholesterol levels in all lipoprotein fractions and total serum lipids, while serum triglycerides were significantly increased compared with RA patients without aLA. Anticardiolipin antibodies as measured by the Venereal Disease Research Laboratory test were not found in any subject in this study. These findings suggest a possible autoimmune origin of dyslipoproteinemia in some patients with active RA.