In order to determine the function of, in vivo, human rennin gene and to establish an animal model for drug inhibitory experiment of human rennin, the transgenic mice were produced via microinjection method by which the mice fertilized ova were injected with the purified human rennin gene. Assay of transgene integration was determined by DIG DNA blotting hybridization and PCR analysis.One mouse among 13 survived mice was the positive transgenic mouse. Integration efficiency was 7.7%. Overall efficiency was 0.3%. Transgene was steadily transfered from generation to generation. The human rennin transgene was found, by RT-PCR, to be expressed in the heart, kidney, and lung of transgenic mice, but not in the liver or skeletal muscle. The mean levels of rennin activity in the plasma of the transgenic mice was also found to be significantly higher than that of the control mice. However, no significant differences were seen in the mean levels of rennin activities in the kidney and heart between transgenic and control mice. These transgenic mice will provide the opportunity to investigate the rennin gene function in circulation (or tissue) rennin angiotensin system, and may, provide an experimental model for testing human rennin inhibitors as drugs.