IPSKCDNA gene(1.8 kbp) encoding rat brain IP3K enzyme contained Not I restric site in open reading frame. The Not I sequence, GCGGCCGC, was converted to GCAGCCGC by site-directed mutagenesis. The mutated IP3KcDNA was digested with EcoR I and ligated with EcoR I-restricted psp72·Not2 vector. The resulting psp72 · Not2-IP3KCDNA was digested with the Not I restriction enzyme and then subcloned into the Not I -digested PZIP · NeoSV(X) mammalian expression vector. The PZIP · NeoSV(X) -IPSKCDNA was transfected into CCL39 hamster lung fibroblast cells. The efficiency of the expressed IPSKCDNA gene was significantly higher than expected generally, not only a mean 5-fold increase in the amount of enzyme, but also 16-fold increase in enzyme activity from tractsfected CCL39 cells by the method of Western blot using anti-lP3K antibodies. Both distribution of IPSK in various rat tissues and biochemical properties were discussed.