The human aspartic proteinases include pepsinogen A, pepsinogen C, cathepsin D, cathepsin E and renin. Comparative analysis of the proteinase genes reveals a high degree of similarity with regard to their respective coding sequences and the location of exon-intron junctions. Despite strong conservation of the regions containing the active site aspartyl groups, genetic polymorphisms have been identified for each of the proteinase genes with the exception of cathepsin D. These genetic polymorphisms are useful for localization of genes on linkage maps as well as determination of gene copy number. The chromosomal location of each aspartyl proteinase has been determined by a variety of gene mapping methods employing recombinant DNA probes including; analysis of somatic cell hybrid mapping panels, in situ hybridization to metaphase chromosome preparations and family linkage analysis with polymorphic markers. Pepsinogen A exhibits the most extensive polymorphism among aspartic proteinases which can be detected by either by protein electrophoresis or by DNA analysis. Southern blot hybridization with respective DNA probes and polymerase chain reaction (PCR) amplification have revealed nucleotide differences located within the coding and noncoding portions of the aspartic proteinase genes. These polymorphisms can be used to investigate potential roles of each proteinase in genetically influenced clinical conditions. The development of additional highly polymorphic markers detected by PCR amplification of divergent nucleotide sequence repeats will greatly assist with documentation of the effect of genetic variation of the aspartic proteinases may have in specific clinical diseases such as ulcer and hypertension.