Cairo and Giza governorates of Egypt.Particulate matter under 2.5 μm in diameter (PM2.5) arises from diverse sources, including tobacco smoke from cigarettes and waterpipes, and is recognized as a cause of acute and chronic morbidity and mortality.To measure PM2.5 in workplaces with different intensities of smoking and varying levels of smoking restrictions.We conducted an air sampling study to measure PM2.5 levels in a convenience sample of indoor and outdoor venues in 2005-2006.Using a calibrated SidePak instrument, 3295 individual measurements were collected at 96 venues. Compared to indoor venues where tobacco smoking was banned (PM2.5 levels 72-81 μg/m(3)), places offering waterpipes to patrons of cafes (478 μg/m(3)) and Ramadan tents (612 μg/m(3)) had much higher concentrations, as did venues such as public buildings with poor enforcement of smoking restrictions (range 171-704 μg/m(3)). Both the number of waterpipe smokers and the number of cigarette smokers observed at each venue contributed significantly to the overall burden of PM2.5.Such data will support smoke-free policies and programs aimed specifically at reducing environmental tobacco exposure and improving air quality in general, and will provide a baseline for monitoring the impact of tobacco control policies.