The relationship between occupational exposures and physician diagnosed asthma were investigated. Data from a random sample of 3,606 adult residents (1,762 men and 1,844 women) of Beijing, China, aged 40 to 69 years pertaining to asthma and exposures to gases and fumes were used. The prevalence of occupational dust exposure was 32%, while gas/fume exposure was 19% for the overall population. The exposures were associated with residential areas, age, education, and the use of coal stoves for heating. No significant relationship was found between smoking status and the exposures. The odds ratios (ORs) of asthma was 3.0 for men and 3.4 for women. The highest ORs were for the shortest exposure duration (1.9 in the 1 to 2 year exposure group). There was an exposure response trend of increasing asthma prevalence with increasing exposure to dusts and fumes, when cumulative exposures of duration and intensity were used. Of 137 identified asthma cases, 89 (65%) also had bronchitis. The adjusted OR for persons excluding those with bronchitis was 1.2 for cumulative dust exposure, and 1.2 for cumulative gas/fume exposure. Logistic regression was used to assess the association of specific dusts or gases/fumes with occupational asthma. The strongest relationship was found with coal (OR, 2.0), organic dusts (OR, 1.9), organic solvents (OR, 2.1), and nonspecific gases (OR, 1.7). The authors conclude that there seems to be an additive effect of gas/fume exposure with dust exposure in causing occupational asthma.