A study of 2500 sera from female blood donors between the ages of 20 and 50 years was undertaken to determine the frequency of antinuclear (ANA), anticytoplasmic (ACA), and antimitochondrial (AMA) antibodies. When sera were tested by immunofluorescence (IF) on HEp-2 cells, 15.9 and 1.1% had ANA titers greater than 1/20 and 1/80, respectively. Analysis of these sera for autoantibody specificity showed: 1.5% antinucleolar, 1.0% anti-nuclear matrix, 0.2% anti-mitotic spindle apparatus, and 0.2% anti-primary biliary cirrhosis nuclear antigen. AMA titers of greater than 1/80 were seen in 2.5% and AMA titers greater than 1/160 were seen in 1.0%. None of the sera had anti-double stranded DNA. Testing of an additional 2500 sera for anti-Sjogren's Syndrome antigen A (anti-SS-A/Ro) revealed a frequency of 22/5000 (0.44%) with the highest frequency (0.72%) being in the 45-50 age group and a relatively high frequency (0.58%) in the 20-24 age group.