The objective was to elaborate the descriptive epidemiology of work-related cases of reactive airways dysfunction syndrome (RADS). Cases of work-related asthma (WRA) were identified in four states in the United States during 1993-1995 as part of the Sentinel Event Notification Systems for Occupational Risks (SENSOR). Information gathered by follow-back interview was used to describe 123 work-related RADS cases and to compare them to 301 other WRA cases whose onset of disease was associated with a known asthma inducer. RADS represented 14% of all new-onset WRA cases identified by the state SENSOR surveillance systems. RADS cases had significant adverse medical and occupational outcomes identified by follow-back interview. In particular, 89% still had breathing problems, 78% had ever sought emergency care and 39% had ever been hospitalized for work-related breathing problems, 54% had applied for worker compensation benefits, and 41% had left the company where they experienced onset of asthma. These values equaled or exceeded the comparable figures for those WRA cases whose onset was attributed to a known inducer. Work-related RADS represents a minority of all WRA cases, but the adverse impact of this condition appears to equal that of other WRA cases.