Three polymerase chain reaction-based assays for the mouse Lepob mutation are described: Dde I site created by the C-->T transversion characterizing Lepob enables positive detection of the mutant allele; positive detection of the wild-type Lep allele is achieved by the use of primer sequence which introduces an A-->C substitution, creating an Msp I site in the normal allele; and an electrophoretic assay which positively identifies the heterozygote.