Reduced physical activity leads, in female mice, to a reduction of the average and maximal life span. The average age at death of the inactive experimental group was 497 +/- 121 days (mean +/- S.D.) compared to 557 +/- 139 days in the active control group, and the six oldest inactive experimental mice died at age 732 +/- 50 days, while the six oldest active control mice died at 890 +/- 52 days. The restriction of mobility was connected with a higher growth rate and a higher body weight in spite of a significant decrease in food intake. In spite of a reduced food intake leading to a reduced whole body metabolism, the results show that mobility restriction shortens life span in female mice.