Data from a community-based four-year prospective study were used to test the hypothesis that heavy physical work is a stronger predictor of low back pain in smokers than in non-smokers. Of 708 working responders without low back pain during the entire year prior to 1990, 562 (79%) completed a questionnaire four years later in 1994. A job involving heavy lifting and much standing in 1990 was a strong predictor of low back pain in smokers four years later [odds ratio (OR) = 5.53, 95% confidence interval (CI) = 1.93-15.84, p < 0.01) after having adjusted for other job characteristics, demographic factors, emotional symptoms, physical exercise and musculoskeletal pain elsewhere. In non-smokers, having a job with heavy lifting and much standing was not associated with low back pain. One explanation may be that smoking leads to reduced perfusion and malnutrition of tissues in or around the spine and causes these tissues to respond inefficiently to mechanical stress.