There are many instances where individual marker genes are of value in breeding programs or genetic studies, or where multiple markers are useful even if their relative positions on a linkage map are not known. In these cases, isozyme markers are of value because they can be detected relatively easily and inexpensively, as well as at an early stage of plant development. Most isozyme polymorphisms have been shown to have a simple genetic basis. Allozymes, the isozyme bands that denote allelic polymorphism at a single locus, display codominant expression, so that plants heterozygous at an isozyme locus may be distinguished from either homozygote. These qualities of isozymes make them useful for the confirmation of hybridity and other forms of pedigree analysis. Isozymes have also been used to tag genes of agricultural importance. Examples of these uses of isozymes will be presented.