Changes in cigarette smoking prevalence by occupation in the United States between 1978 to 1980 and 1987 to 1990 were examined. Data on smoking habits and occupation were taken from the 1987, 1988, and 1990 National Health Interview Surveys (NHISs) and compared with data obtained in the 1978, 1979, and 1980 NHISs. The data were analyzed according to occupation using occupational codes utilized in the 1970 and 1980 censuses. The 1978 to 1980 NHIS data set included 28,640 employed persons 17 years or older. The 1987 to 1990 data set included 82,358 employed persons 18 years or older. During 1987 to 1990 the overall prevalence of cigarette smoking by occupational group was: blue collar workers, 39.2%; service workers, 34.5%; white collar workers, 24.2%; farm workers, 22.8%; and persons not in the labor force, 22.9%. By gender, the overall prevalence of smoking was 36.0% for males and 33.6% for females. Compared to the 1978 to 1980 data set, the prevalence of cigarette smoking decreased by 8.0% in male white collar workers, 7.0% in female white collar workers, 5.1% among male blue collar workers, and 4.8% in male service workers by 1987 to 1990. These decreases were statistically significant. Among males, the occupational groups showing the largest statistically significant decreases in cigarette smoking prevalence were sales workers, managers and administrators, transportation equipment operators, and professional and technical personnel, the decreases amounting to 10.5, 8.7, 7.5, and 6.7%, respectively. Among females, the largest significant decreases in smoking occurred among managers and administrators, professional and technical personnel, clerical workers, and sales workers, the decreases amounting to 9.9, 8.0, 4.8, and 4:7%, respectively. The authors conclude that cigarette smoking remains more common among blue collar and service workers than white collar workers; however, since 1978 to 198O, the differences in smoking prevalence by occupation have widened. Smoking cessation should be encouraged in certain subpopulations such as blue collar workers and those with less education.