Inactivity is the risk factor with potentially the greatest public health impact, according to the 1989 U.S. Preventive Services Task Force report. Our study reports changes in subjects' physical fitness level after simple changes aimed at enabling community members to adopt more easily active lifestyles. Simple environmental and social alterations occurred at a San Diego Naval air station. We administered to a cohort of active-duty personnel from within this community (n = 1,609) both a physical readiness test (PRT) and a lifestyle questionnaire at baseline and at one year. The PRT consisted of a 1.5-mile timed run, sit-ups, push-ups, and percentage body fat components, and the questionnaire addressed demographics, current exercise behavior, and attitudes toward exercise. We took similar measures within a comparison community cohort (n = 217) and within a Navy-wide sample cohort (n = 546). Both overall PRT category and 1.5-mile run time improved significantly (P less than .05) over time in the intervention community (0.3 category points and 18 seconds, respectively). The increase was significantly greater (P less than .01) than in either the control community or the Navy-wide sample. Subgroup analysis showed that, in the intervention community, 12.4% failed the overall fitness test in 1987, but only 5.1% failed in 1988. Similarly, the 1.5-mile run failures decreased from 8.4% to 4%. Reported leisure time kilocalorie expenditure showed no significant improvement. This simple program successfully improved fitness performance. The improvement was distributed throughout the community and included those who were substandard at baseline. Similar programs could easily be adopted in a variety of communities.