It was observed that both glutamic oxalacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) activities were significantly increased in different tissues of both rats and guinea pigs, during a short period of altitude exposure, as well as in acclimatized animals. Interestingly, it was found that oral administration of glucose showed no such significant change at either sea level or in a hypoxic condition. Studies on the activity of GOT and GPT in different tissues of normal guinea pigs showed a little change in liver and brain during short periods of exposure. Kidney and heart showed a significant increase in GOT activity without any change in GPT activity. Increased activities were observed in all the tissues of the acclimatized animals. Of both unexposed and acclimatized animals, there was no change in the enzyme of unexposed and acclimatized animals except in heart following injection of thyroxine (16 micrograms X kg-1), but the enzyme activities were most pronounced in scorbutic animals.