The aim of this study was to identify occupational risk groups which might usefully be targeted for occupational asthma surveillance and control, using a community-based case-control approach. Data on previous and current occupations held by subjects were analyzed for 787 adult patients with bronchial asthma and 1591 nonasthmatic patient controls, aged 20-54 years, belonging to the three major races (Chinese, Malays, and Indians) in five outpatient primary care polyclinics. Odds ratios (OR) and 95% confidence intervals (95% CI) of association were adjusted for sex, age, race, smoking, and clinical atopy. No associated risks of asthma were found for clerical or sales workers in general. Significantly reduced risks of association with asthma were found for professional, technical, administrative, and managerial occupations (OR, 0.62; 95% CI, 0.47-0.82). The associated risks of asthma were generally elevated for service workers (OR, 1.35; 95% CI, 1.04-1.74) and manufacturing production and related workers (OR, 1.49; 95% CI, 1.23-1.81). Among them, increased risks were observed for cleaners, particularly municipal cleaners and sweepers (OR, 1.91; 95% CI, 1.22-2.99), textile workers (OR, 5.83; 95% CI, 1.93-17.57), garment markers (OR, 1.61; 95% CI, 1.01-2.58), electrical and electronic production workers (OR, 1.36; 95% CI, 1.06-1.75), printers (OR, 2.24; 95% CI, 1.17-4.31), and construction/renovation workers (OR, 2.24; 95% CI, 1.30-3.85). The odds ratio of association of asthma with exposures in service and production-related occupations overall, relative to the "nonexposed" reference group of nonmanual professional/technical, administrative/managerial, clerical, and sales occupations, was estimated to be 1.72 (95% CI, 1.36-2.19); the estimated population attributable risk was 0.33 (95% CI, 0.22-0.44).