Chicken DNA has been digested with restriction enzymes and the size distribution of the DNA fragments containing ovalbumin specific sequences has been examined after separation of the fragments on agarose gels and transfer to nitrocellulose sheets. Hybridisation with terminally 32P-labelled ovalbumin mRNA fragments or with RNA populations transcribed from the DNA of a hybrid plasmid containing ovalbumin sequences was used to locate the DNA fragments coding for ovalbumin. Digestion with enzymes which do not cut within the portion of the ovalbumin gene synthesised from ovalbumin messenger RNA in vitro has shown the presence of several defined fragments carrying ovalbumin specific sequences. Possible explanations of these observations are discussed.