A group of 255 blood donors was analyzed for the presence of serum autoantibodies, e.g., antinuclear antibodies, smooth muscle antibodies, antimitochondrial antibodies, antiparietal cell antibodies and antireticulin antibodies by indirect immunofluorescence microscopy. The 37 (15%) who had autoantibodies underwent examination and extended laboratory investigation. We found no strong evidence of disease in any of the blood donors with autoantibodies.