The effect of intense physical training on the bone-mineral content of young adults who are unaccustomed to physical activity has not yet been established. In this study, 268 male recruits, eighteen to twenty-one years old, were evaluated before and after fourteen weeks of strenuous physical training. The bone-mineral content of both legs at the level of the distal third of the tibia in each individual was measured using single-beam photon absorptiometry. The subjects started their training with equal values for bone-mineral content in both legs. During the training period, the average bone-mineral content of the left leg increased by 11.1 per cent and that of the right leg, by 5.2 per cent. In the group of subjects who did not complete the training course, mainly because they incurred stress fractures, the increase in bone-mineral content was significantly less than the increase in those who completed the program. This study indicated that in young adults a high level of loading of bone results in either a stress fracture or a rapid increase in bone-mineral content.