This experiment was performed to determine the genetic stability of FGS/Kist mouse strain through biochemical and immunogenetical monitoring methods. In biochemical monitoring by staining after electrophoresis, fifteen biochemical markers, alkaline phosphatase-1, carbonic anhydrase-2, esterases-1, 2, 3, glucose-6-phosphate dehydrogenase-1, glucose-phosphate isomerase-1, hemoglobin beta-chain, isocitrate dehydrogenase-1, lactate dehydrogenase regulator, malic enzyme supernatant, major urinary protein, peptidase-3, phosphoglucomutase-1 and transferrin were all identical types among six mice from each of the F25/F26 generations. In the immunogenetical monitoring followed by the cytotoxic test, histocompatability-2D and -2K were shown to be 'k' type. No differences were found between F25 and F26 generations of FGS/Kist mice. these results suggested that FGS/Kist mice are genetically stable.