Transcription of the HIV-1 provirus genome is regulated by a complex interplay between viral regulatory proteins and cellular transcription factors that interact with the viral long terminal repeat (LTR) region of HIV-1. However, several cellular transcription factors have been identified that can interact with the HIV-1 LTR; the significance of all of these factors is not clearly understood. In this study we have characterized the LTR region of different subtypes of HIV-1 with regard to nucleotide sequence and promoter activity. The LTR regions of HIV-1 from peripheral blood mononuclear cells of 29 infected individuals originating from 10 different geographical regions were sequenced and further analyzed for promoter/enhancer activity in transient transfection of HeLa cells, in the context of a reporter gene and in the context of the complete virus genome. We found several subtype-specific LTR sequences of the various HIV-1 strains, such as an insertion that created a potential third NF- kappa B site in the LTR of the subtype C strains. The USF-binding site in the NRE also contained subtype-specific sequences. Interestingly, the promoter/enhancer activities of the subtype C LTRs were higher than the activities of the other subtypes analyzed here (subtypes A, B, D, E, and G), suggesting that the potential third NF- kappa B site may confer higher LTR activity or that the subtype C NRE may be less potent. Thus, our data suggest that genetic diversity of the LTR may result in HIV-1 subtypes with different replicative properties.