Bovine antigens are routinely used in indirect ELISA tests to detect autoantibodies against extractable nuclear antigens (ENA). Here we investigate the difference in clinical sensitivity between ELISA tests prepared with native human and bovine antigens. SSA and SSB were obtained from spleen and nRNP/Sm complex from thymus. Each antigen was extracted with the same immunoaffinity column. ELISA tests with human and bovine antigens were set up under the same conditions of clinical specificity established on 50 blood bank donors. Of 109 random SLE and Sjogren's syndrome sera 49% and 35% were positive, respectively, for human and bovine SSA, 26% and 16% for SSB. Of 98 random SLE sera 52% and 41% were positive for human and bovine nRNP/Sm, respectively. A few specimens reacted only with bovine antigens, probably false positive reactions. The relative clinical sensitivity for all specimens identified as positive by human and/or bovine antigens was significantly higher with human than with bovine SSA, (93% vs 67%; P<0.001, chi2), SSB (93% vs 50%; P<0.001), and for nRNP/Sm (96% vs 75%; P<0.01). However, for values that exceeded 2.5-4 times the upper normal limit, the levels were similar for human and bovine antigens. We concluded that native human antigens offer clinical sensitivity superior to native bovine antigens for the measurement of anti-ENA antibodies by ELISA.