An src/yes-related novel gene named syn (SYN in human gene nomenclature) has been identified in the human genome on chromosome 6 and characterized by molecular cloning. Nucleotide sequence analysis of cDNA clones showed that the c-syn gene could encode a protein-tyrosine kinase that is very similar in primary structure to the v-yes and human c-src proteins. A 2.8-kilobase transcript of the c-syn gene, which differs in size from those of the c-yes, c-src, and c-fgr genes, was observed in various cell types. These results show that syn is a new member of the tyrosine kinase oncogene family.