We have recently identified in SLE sera antibodies against phosphotyrosine. They were also detected in normal sera and gammaglobulin preparations, suggesting that they belong to natural autoantibodies.In this paper, the occurrence of anti-idiotypic antibodies against anti-phosphotyrosine antibodies, in the above mentioned samples, is investigated. In order to identify these anti-idiotypic antibodies ELISA, immunoprecipitation and immunoblotting are performed.Our data demonstrate the presence of anti-idiotypic antibodies specific to anti-phosphotyrosine antibodies in SLE sera as well as in normal sera, suggesting that these anti-idiotypic antibodies are also auto-anti-idiotypic antibodies. The densitometry of immunoblots reveals significantly higher levels of anti-idiotypic antibodies in SLE sera. Based on the competition inhibition studies we conclude that some of these anti-idiotypic antibodies belong to beta/gamma type.