Three components of environmental tobacco smoke, namely, carbon monoxide, particulate matter and nicotine were monitored over 30 minute intervals in travel, work, home and leisure situations. Around 3,000 sets of measurements were made with approximately equal numbers in smoking and non-smoking environments. Mean concentrations of these components were calculated for the total study as well as for different regions, situations and locations. Although some slight regional variations were evident, most differences were associated with the type of location sampled. Carbon monoxide levels were not significantly different between non-smoking and smoking environments for each of the four types of situation, whereas particulate matter and nicotine were higher where smoking occurred.