A cross-sectional study of 31 textile factories in Lancashire revealed a marked decline in the prevalence of byssinotic symptoms since the industry was last surveyed comprehensively in the 1960's. This was unparalleled by a similar decrease in dust levels, but airborne bacteria vanished in all but three of the factories. Despite the questionnaire from the workers (182 among 4656 people) prevalence was still found to be statistically significantly associated with years of exposure to cotton dust, ethnic origin, workroom of employment, quality of cotton used and the logarithm of 'inhalable' dust determined in the personal breathing zone. A good dose-response relationship was established for the prevalence of both byssinosis and chronic bronchitis and dust exposure. The observed associations are probably a reflection of past rather than present conditions.