The heterocyclic secondary amine piperazine is known to cause asthma. In a cohort of 602 workers, employed during the period 1942-1979, at a chemical industry where piperazine is handled, a study conducted by means of a mailed questionnaire showed a strong exposure-response relationship as to frequency of work-related airway symptoms indicating asthma. In the most exposed group about a third of the workers had experienced such symptoms. Age, length of employment, smoking habits, and previous work-related asthmatic symptoms, but not atopy, modified the response. Further, there was an association between piperazine exposure and chronic bronchitis. In the most exposed group every fourth subject had chronic bronchitis. The frequency was modified by smoking habits; atopy was a confounder. Although many subjects, especially high-exposed ones, left work because of airway symptoms, there was no difference in occurrence of airway symptoms between former and present employees, ie, no "healthy worker selection" ("survivor population effect").