During 35-day hypokinesia rat spongy bone in the tibia and vertebrae varied in two phases. The first phase (up to 15 days) was induced by a stress-reaction and the second phase by adaptation to hypokinesia. Under the influence of subcutaneous injections of hydroxydimethyl aminopropylidene biphosphonate (AMOK) at a dose of 0.01 mg/kg/day bone changes disappeared: throughout the study spongy bone mass remained as in controls. AMOK administration at a dose of 5 mg/kg/day 10 days prior to hypokinetic exposure did not eliminate its inhibitory effect although the initial bone mass was 1.5-2 times higher than in the controls. However at the adaptation phase (beginning with day 15) bone mass increased, reaching the baseline. This indicates a decline in bone sensitivity to muscle unloading. It is concluded that AMOK modifies bone responses to various hypokinetic factors.