Embryonic chick feather keratins are a family of homologous polypeptide chains. The mRNA coding for these has been obtained in a pure state and transcribed into complementary DNA (cDNA) using the reverse transcriptase from avian myeloblastosis virus. Studies on the kinetics of hybridisation and reannealing of cDNA indicate that there are 25-35 different keratin mRNA species in the embryonic chick feather, and a total of 100-240 keratin genes in the chick genome. Each keratin gene contains both a unique and a repetitive sequence. It is proposed that the repetitive sequences are the keratin coding sequences and that the unique sequences correspond to untranslated regions.