Summary:The mating of narcoleptic Doberman pinschers yielded 30 puppies in five litters, all of which developed the disease between 1 and 4 months of age. Pedigrees of the Doberman probands are indicative of an autosomal recessive mode of transmission. An analysis of the pedigree of five affected Labrador retriever littermates suggests a similar mode of transmission. Crosses of affected dogs in two other breeds (miniature poodles and beagles) have resulted in all-unaffected F) generations, thus allowing rejection of the simplest genetic hypothesis of a fully penetrant autosomal or sex-linked dominant or recessive gene.