We have characterized the ability of various human autoimmune sera to react with RNA polymerase II transcription factors. One serum, which strongly inhibited transcription in a cell-free system, was shown to contain antibodies directed against human TFIIB. The serum did not show reactivity against the other general transcription factors, including human TBP, TFIIE and TFIIF. The inhibition of transcription was directly attributable to depletion of TFIIB activity, as demonstrated by reconstitution of activity with recombinant TFIIB. It has long been recognized that components of the RNA processing machinery are major human autoantigens. The present results show that at least one general transcription factor required for messenger RNA synthesis is an autoantigen as well.