The determinants of physical activity in adults were explored in this study. Explanatory variables included perceived benefits of and perceived barriers to physical activity, and perceived self efficacy for physical activity. Inactive participants were asked to identify barriers to activity, and active participants cited cues prompting them to adopt a physically active lifestyle. Data were collected from 137 adults obtained from work sites, an evening college program, and church groups. Overall, participants were physically active. Self efficacy was the only variable to predict physical activity. Race (i.e., being White) and body mass index (i.e., being overweight) explained perceived barriers to activity. The primary reason for inactivity was lack of time, and the most frequently cited cues to activity were dissatisfaction with one's weight or appearance. Few nursing studies have attempted to increase participants' levels of self efficacy. However, the occupational health nurse is in a unique position to increase workers' perceived self efficacy for activity and, in turn, their activity levels.