Negative calcium balance and bone loss occurring with immobilization and hypokinesia have been attributed to a lack of weight bearing on bones. The effects of weight-bearing exercise for promotion of calcium balance after hypokinesia were examined. Rats were randomly assigned to either hypokinetic suspension for 28 d or to a control sedentary group, free to move about their cages at will. After 28 d, the rats in each group were randomly subdivided to either post-hypokinetic forced running (HR), post-hypokinetic sedentary (HS), control forced running (CR), or control sedentary (CS) groups. Net calcium balance was then determined for 25 consecutive days. Net calcium balance of HR was negative for the first 5-d period of recovery and then became positive; that of HS was negative for 25 d; that of CR and CS remained essentially positive. Net calcium absorption paralleled net calcium balance. Forced running was effective in reestablishment of positive net calcium balance after 28 d of decreased weight bearing.