Background: It has been hypothesized that a period of rest from running in the early weeks of basic military training will prevent stress fractures among recruits. Design: Modification of running schedules in companies of Army recruits undergoing basic military training was assigned. Setting/Participants: Six male training companies were enrolled and followed during their 8 weeks of basic military training at Fort Bliss, Texas, in summer/fall 1989. Intervention: Intervention companies were asked to rest from running during the second, third, or fourth week of basic military training. Main outcome measures: Data were collected from questionnaires, anthropometric measurements, Army physical fitness tests, company training logs, and medical record abstraction of all clinic visits. Conclusions: The study provided no evidence for a protective effect on overuse injuries of resting from running for 1 week early in basic military training. There was varied physical training among the companies, however, with variation of injury rates that likely related to factors other than the intervention. (C) 2000 American Journal of Preventive Medicine.