This report describes the first set of coordinated time-series studies ever undertaken in Asian cities: four time-series studies of the health effects of air pollution in Bangkok, Hong Kong, Shanghai, and Wuhan. These studies were intended to help bridge the gaps between studies conducted in different locations around the globe. They explored key aspects of the epidemiology of exposure to air pollution in each location - issues of local as well as global relevance - including the effects of exposure at high concentration and at high temperatures, the potential influence of influenza epidemics on the relations between air pollution and health, and the ways in which social class might modify risks associated with air pollution. Research Report 154 comprises the four individual studies by Kan et al. (Shanghai), Qian et al. (Wuhan), Vichit-Vadakan et al. (Bangkok), and Wong et al. (Hong Kong), a combined analysis conducted by Wong on behalf of the PAPA teams, and commentaries by the HEI Health Review Committee.