The effects of hypergravitation, hypodynamia and their combined action during 6 days on the striated muscle ultrastructure of m. gastrocnemius in Japanese quails were studied. Cockerels at the age of 48 days were divided into 5 groups. They were exposed to hypergravitaty of 2 G in a centrifuge, hypodynamia, and combined hypergravitaty and hypodynamia, in the centre of a centrifuge, and they were compared to a control group. Comparing the morphological picture of striated muscle of Japanese quail in all experimental groups, we concluded that the action of different stress factors during 6 days did not cause substantial changes in the basic morphological structure, except for the groups placed in the centre of the centrifuge and the one with combined hypergravitaty and hypodynamia where they had been most strongly exposed to loading.