The changes of contents of inositol phosphates in Phenylephrine stimulated contraction of aorta from both 3 month and 20 month Wistar rats were studied by means of Bioassay method, and [3H]-myo-inositol labelling, ion exchange chromatography. The results were as follows: (1) In both resting and PE-activated arteries, IP took the greatest part (67%-83%) in total amount of inositol phosphates and the contents of IP, IP2 and IP3 were significantly higher in 20 month rat aorta than that in 3 month rat. (2) There is an age-related reduction in aortic contraction in Ca(2+)-free buffer and Ca(2+)-containing buffer. These results suggest that there is an age-related difference in IP metabolism pattern and pathway, and that IP metabolism in old rat is obviously active, but the Vascular response is apparently low.