The peroxidase (CPX, PER), α-amylase (α-AMY), acid and alkaline phosphatase (PHE, PHS) and esterase (EST) zymogram phenotypes of 'Chinese Spring' wheat, 'Betzes' barley and a number of presumptive 'Betzes' chromosome additions to 'Chinese Spring' were determined. It was found that five disomic chromosome addition lines could be distinguished from one another and from the other two possible lines on the basis of the zymogram phenotypes of these isozymes. The structural genes Cpxe-H1 and Cpxe-H2 were located in 'Betzes' chromosome 1, the Perl-H5 and Perl-H6 in chromosome 2, the α-Amy-H2 and α-Amy-H3 in chromosome 7, the Phs-H5 and Phs-H4 in chromosomes 1 and 3 respectively, the Phe-H2, Phe-H3 and Phe-H4 in chromosome 1, the Phe-H1 in chromosome 3, the Ests-H4, Este-H2 and Ests-H6, Este-H8 in chromosomes 1 and 3 respectively and the Estl-H10 and Estl-H2 structural genes were related to chromosomes 3 and 6 respectively. These gene locations provide evidence of homoeology between 'Betzes' chromosomes 1, 2, 3, 6 and 7 and the rye chromosomes 7, 2, 3, 6 and 5, respectively, and also between 'Betzes' chromosomes 1, 2, 3, 6 and 7 and the 'Chinese Spring' homoeologous groups 7, 2, 3, 6 and 5, respectively.