We have determined the total coding sequence of human c-yes, a non-receptor type protein-tyrosine kinase gene, and found that the c-yes gene closely resembles the c-src gene. Recently, two new genes, syn and lyn, were found to encode proteins closely related to the yes product. In addition, we also determined the partial sequence of fgr. These genes together with lck reported by two American groups have very closely related structures and are thought to compose a closely related group of non-receptor type protein-tyrosine kinases. Partial analysis of the structures of these genes indicated that they have identical splicing junctions at all sites so far examined. On the other hand, the erbB-1/EGF (epidermal growth factor) receptor gene and the erbB-2/neu gene have completely different splicing junctions from those of the above gene group even in the kinase domain, although these genes also have protein kinase activity specific for tyrosine residues and the erbB-1 and -2 genes share splicing sites. These results suggest that the genes of the group of six non-receptor type kinases and those of the erbB-1 and erbB-2 gene group are descendants evolved by duplication of two distinct ancestor genes and are members of two distinct multi-gene families. The genes coding for protein kinases may be members of a super-family including multiple distinct gene families.