Two days before launch of the biosatellite Cosmos-2044 five rats were exposed to surgical intervention: their fibulas were cut bilaterally. The purpose was to study the effect of microgravity on bone fracture healing. Histologically and histomorphometrically it was demonstrated that healing was inhibited; as a result, bone callus was poorly developed and bone fragment consolidation was inadequate. An increase in the relative volume of osteoid and a simultaneous decrease in the number and activity of osteoblasts point to mineral disorders of newly formed bone in microgravity. Study of untreated tibia showed that exposure to microgravity led to osteoporosis of proximal metaphyses. This osteoporosis was produced by inhibited neoformation and enhanced resorption of bone. Comparative analysis of injured fibula and untreated tibia of rats exposed to real microgravity for 14 days or tail suspended demonstrated similarity of changes. This indicates that tail suspension can be viewed as an adequate simulation of microgravity with respect to changes in hindlimb bones.