The study was a cross-sectional survey, including retrospective work history data. A random sample was conducted of 40 board certified pulmonologists in Northern California enrolling persons with asthma. Pulmonologists maintained a log of all persons meeting a clinical definition of asthma presenting to their offices for treatment over a one month period. A total of 601 subjects with any history of laborforce participation were interviewed by a trained survey worker in order to assess severity of disease using a severity scale based on symptoms, medications, and past-asthma history. The computer-assisted, telephone-administered interviews used established survey instruments to assess psychosocial variables, smoking exposure and work history.