A surveillance programme of work-related hazards and diseases (PRiOR) was developed in the Piedmont region of Italy during 1996-97, including an active surveillance system for asthma. Incidence estimation, early information to the patient, identification of responsible workplaces were the main objectives of the programme. A network of 18 clinical centers (allergologists, chest physicians, occupational physicians) from whole the Piedmont region provides information on newly diagnosed cases to a surveillance center that receives and analyzes reports and disseminates surveillance results to clinicians and occupational health and safety services, responsible for intervention. Between 1 March 1996 and 31 December 1997 67 new cases were reported, which corresponds to an incidence rate of 24 (C.I. 95%: 18-30) per million workers per year. The incidence was higher among bakers (540 per million), among workers employed in the leather and shoe industry (214 per million), in health care services (205 per million), in the pharmaceutical industry (199 per million) and among hairdressers (196 per million). The agents to which workers were exposed at the time of diagnosis were generally well recognised (latex 51%; flour 27%). Procedures and results of the PRiOR programme are comparable with those from surveillance systems operating in other countries. Nevertheless, continued efforts are needed to increase the proportion of collaborating physicians, to standardize the use of tests for diagnosis and to improve the communication between clinical centers and occupational health and safety services. Like most surveillance systems based on similar methods, PRiOR underestimates the true incidence of work-related asthma in the Piedmont Region. Despite this limitation, the PRiOR active surveillance system of work-related asthma has proven successful in identifying more new cases of asthma than official sources do. It can therefore be permanently implemented in the prevention system regional.