It was recognized that recombinant inbred strains are a very powerful system for the study of the genetics of hypertension, linkage analysis and gene mapping. Such set of recombinant inbred strains has been developed in the cooperation of Prof V. Kren and Dr. M. Pravenec in Prague. These recombinant inbred strains were used to search for the genes of spontaneous hypertension and to test the phenotypic differences. It was found that 1) the major histocompatibility complex of the rats showed a significant association with blood pressure, 2) the restriction fragment length polymorphism in kallikrein gene family as well as renin gene cosegregated with blood pressure, 3) Na+ leak in red blood cells cosegregated with blood pressure, 4) the relative heart and kidney weights are not closely related to mean arterial pressure and 5) the platelet aggregation and blood pressure are independent traits. The results indicate the usefulness of recombinant inbred strains in the analysis of the relationship between phenotype and genotype.