This study of 29 blue and 57 white collar workers (mean age 50 and 51 yr) investigated behavior and the level of subjective stress and objective strain during work and leisure time. Physiological and psychological parameters as well as behavioral activities were assessed simultaneously using a special ambulatory monitoring device capable of storing 23 h records. Total strain was operationalized by heart rate (HR), physical strain by physical activity, emotional strain by non-metabolic HR, and mental strain by HR variability. Analysis of the physiological parameters for the working hours from 8 to 16 h revealed di!erences between the hours for physical activity, HR, and non-metabolic HR but not for HR variability. Between 12 and 13 h, physical activity was somewhat lower and non-metabolic HR higher, presumedly caused by the lunch break. Physical activity and HR were higher for blue than white collar workers due to the di!erent tasks of the workers. Self-reports of excitement and enjoyment during the working hours showed no main e!ects in the MANOVA. Comparison between total working time and leisure time revealed lower physical activity and HR but higher non-metabolic HR for leisure time. In the self-reports, however, leisure time was rated less exciting and more pleasant than working time. There was no indication of higher emotional strain for one or the other group, but mental strain at work was somewhat higher for the blue collar workers. In a questionnaire, white collar workers reported having signi"cantly more stress at work and outside work than blue collar workers. Analysis of the behavior during leisure time (physical activity, activity, social contacts) showed only minor di!erences between the groups.