Vimentin is an intermediate filament protein normally expressed in cells of mesenchymal origin. The promoter of the human vimentin gene (-1416 to +73) was shown to contain two positive-acting regions, separated by a negative region, and at least eight GC-boxes as determined by sequence homology (Rittling, S.R., Baserga, R., 1987. Mol. Cell. Biol. 7, 3908-3915). We have analyzed the region -900 to +41 for protein binding by in vivo footprinting experiments using ligation-mediated PCR. For the various GC-boxes, we detect protein binding only to that GC-box (at position -64 and -55) closest to the transcriptional start site. Transient transfection assays of various vimentin 5'-end fragments and mutations thereof fused to the reporter gene cat indicate that this sequence is indispensable for promoter function regardless of the inclusion of upstream DNA sequences. In vitro binding studies confirm that this region binds protein specifically. We suggest that this GC-box and its binding factor are required for regulated expression of the human vimentin gene.