The classic diseases of dusty occupations may be on the decline, but this is not the case for chronic nonmalignant lung disease characterized by airflow limitation. This group of diseases, almost certainly multifactorial in etiology, occurs in those engaged in dusty occupations as well as in those who are not. Among the environmental factors concerned, cigarette smoking is clearly one of the most important, but occupational exposures are increasingly implicated. It is also clear that not all with similar exposures are affected, pointing to the importance of host or personal factors. Evidence is now accumulating in support of what has been called the Dutch hypothesis. This explanation of the natural history of chronic airflow limitation suggests that an "asthmatic tendency" is a necessary factor whether the putative exposure is to cigarettes or to other airborne pollutants. Further research should therefore be directed towards clarifying the relationships of acute and chronic airway dysfunction in response to airborne pollutants of all types.