Data are tabulated on the number of nomenclature current abbreviations, the occurence of multiple gene loci and corresponding polypeptide chains, and chromosomal assignment of 114 enzymes. Gene dose effect measurement is dependent upon several properties of the enzyme which are also listed: tissue and subcellular distribution, subunit number, interloci hybrids, genetic polymorphism, qualitative and quantitative methods of detection. The possibilities and limits of the concept of a gene-dose relationship, for the detection of carriers of chromosomal aberrations, and also for chromosomal assignment are discussed.