Human fibronectin (FN) genomic clones were isolated by screening a human genomic library with a 75-base oligonucleotide. The sequence of the oligonucleotide corresponds to a region near the 5' end of the human FN cDNA clone pFH6 that contains the amino-terminal coding sequences but does not extend to the 5' end of the mRNA [Kornblihtt, A. R., Umezawa, K., Vibe-Pedersen, K. & Baralle, F. E. (1985) EMBO J. 4, 1755-1759]. The 5' end of the FN gene is found on a 3.7-kilobase-pair EcoRI fragment that contains about 2.7 kilobase pairs of flanking sequence. The first exon is 414 base pairs long, with a 5' untranslated region of 267 base pairs. As deduced on the basis of the position of the initiation codon, FN is synthesized with a 31-residue amino acid extension on the amino terminus that is not present in the mature polypeptide. This amino-terminal extension appears to contain both a signal peptide and a propeptide. The first 200 base pairs of 5'-flanking sequence is very G + C rich. Upstream of this the sequence becomes relatively A + T rich. The sequence ATATAA is found at -25 and the sequence CAAT is present at -150. The sequence GGGGCGGGGC at -102 exhibits homology to the binding site for the transcription factor SP1, and the sequence TGACGTCA at -173 exhibits homology to 5'-flanking sequences important for induction by cAMP.