We have investigated the expression levels of the TATA-binding protein (TBP) and several TBP-associated factors (TAFIIs) in differentiated adult mouse tissues. Immunoblots performed using monoclonal antibodies show that there are considerable variations in the levels of TBP and many TAFII proteins present in various tissues. Consequently, the relative levels of TAFIIs and TBP vary significantly from one tissue to another. TBP and several TAFIIs are overexpressed in both testis and small intestine, while in marked contrast, many of these proteins, including TBP itself, were substantially down-regulated in nervous tissues and in the heart. These tissues do, however, show a high expression level of the TBP-like factor, which thus may represent an alternative factor for the specialized transcription program in some differentiated tissues. While there are significant variations in the levels of TAFII28 protein, reverse transcription-coupled polymerase chain reaction shows similar expression of the TAFII28 mRNA in different tissues. The variations in TAFII28 protein levels therefore result from post-transcriptional regulatory events.