The 5'-end of the human transforming growth factor-beta 1 gene (TGF-beta 1) was isolated from a human leukocyte genomic DNA library. Analysis of the transcriptional start sites of human TGF-beta 1 mRNAs by S1 mapping and primer extension revealed two major start sites 271 nucleotides from one another; several minor sites were also identified. DNA sequence analysis showed that the promoter region contains neither a "TATA" box nor a "CAAT" box, is very G+C rich, and contains 11 CCGCCC repeats. Seven putative binding sites for the transcription factor Sp1 were also identified. To determine the location of sites that may be important for the function of the TGF-beta 1 promoter, we joined the 5'-end of the TGF-beta 1 gene to the coding region for chloramphenicol acetyltransferase. The chimeric gene produced high levels of chloramphenicol acetyltransferase activity in transfected HT-1080, AKR-2B, and A-549 cells. Sequences responsible for both promotion and inhibition of transcription were located in the region extending from 1400 to 300 base pairs upstream of the first major TGF-beta 1 transcriptional start site. The 130-base pair fragment located between 453 and 323 base pairs upstream of this start site contains positive regulatory activity in all cells tested. A second promoter activity was identified in the region between the two major transcriptional start sites. These findings revealed a complex pattern of regulation of human TGF-beta 1 gene expression.