The fibroblast growth factors (FGFs) play important roles in morphogenesis, angiogenesis, tissue remodeling, and carcinogenesis, Human FGF-SO has been cloned and characterized in this study. FGF-SO encodes a 211-amino-acid polypeptide with the FGF-core domain. A strong hydrophobic region was found in the FGF-core domain of FGF-20; however, no typical N-terminal signal sequence was found in FGF-20, just as in FGF-9 and FGF-16. Total amino acid identities are as follows: FGF-20 vs FGF-9, 71.6%; FGF-20 vs FGF-16, 66.2%; FGF-9 vs FGF-16, 72.4%. Phylogenic analysis indicated that FGF-20, FGF-9, and FGF-16 constitute a subfamily among the FGF family, FGF-20 mRNA of 2.4 kb in size was detected in colon cancer cell line SW480 by Northern blot analysis. Lower levels of FGF-SO mRNA were detected in human fetal tissues and primary cancers by cDNA-PCR. The nucleotide sequence of FGF-20 cDNA is split into three parts in the human genome sequence of the chromosome 8p21.3-p22 region (Accession No. AB020858). These results indicate that the FGF-20 gene, located on human chromosome 8p21.3-p22, consists of three exons, Compared with the nucleotide sequence of FGF-20 cDNA determined in this study, one nucleotide deletion and one nucleotide substitution in the putative coding region mere identified in human genome sequence AB020858.