The purpose of this study was to identify the strengths and limitations of using portable peak flowmeters to document suspected cases of occupational asthma that were reported to a statewide surveillance project. The New Jersey Department of Health conducts surveillance for occupational asthma as part of the federally sponsored Sentinel Event Notification System for Occupational Risks (SENSOR). Between May 1988 and January 1990, 70 cases were reported voluntarily by physicians. Subjects who were still employed in suspected work sites were requested to test themselves for at least 15 days, using portable peak flowmeters to generate serial measurements of their peak expiratory flow rate (PEFR). For each of the 14 subjects who were successfully tested, the PEFR data provided valuable information about their asthma-work association. However, a large number of subjects whose cases were reported (56) either could not be tested or were not successfully tested. The proportion of subjects completing the test would probably improve if it were conducted when their conditions were first diagnosed. Accordingly, the collection of serial peak flow measurements to document occupational asthma would best be initiated by the treating physician when the patient first sought care, rather than waiting until after the case was reported to the state health department.