The mouse alpha-fetoprotein mRNA is the product of a single-copy gene whose mRNA coding sequences are represented discontinuously in the genome. Several EcoRI genomic fragments which contain portions of the alpha-fetoprotein gene have been cloned using the EK2 vector lambda gt WES . lambda B. In addition, a mouse genomic library has been screened to obtain a 15.75-kilobase segment of DNA that includes more than 85% of the alpha-fetoprotein coding sequence. Analyses by restriction endonuclease mapping and electron microscopy showed that the mRNA sequence is interrupted by at least 11 intervening sequences which occupy 90% of the cloned DNA.