The objective of this work was to determine whether the prevalence of respiratory symptoms differed among workers exposed to different types of metal-working fluids. As part of a mandatory surveillance system for occupational illness, from 1988-1994, the Michigan Department of Public Health received, 86 occupational disease reports of work-related asthma secondary to exposure to metal-working fluids. As part of a public health program, follow-up industrial hygiene inspections, including medical interviews of the workforce, were performed at companies where the reported cases had become ill. Metal-working fluids were the second most common cause of work-related asthma reported in the state. Most of the reports were from the automobile industry. Follow-up inspections were conducted at 37 facilities where the individuals with work-related asthma had worked. Seven hundred and fifty-five workers at these facilities were interviewed. Only one facility was above the allowable oil mist standard. Despite the exposure levels being within the legal limits, approximately 20% of the fellow workers of the reported cases had daily or weekly respiratory symptoms suggestive of work-related asthma. Workers exposed to emulsified, semisynthetic, or synthetic machining coolants were more likely to have chronic bronchitis; to have visited a doctor for shortness of breath; to have visited a doctor for a sinus problem; to be bothered at work by nasal stuffiness, runny nose, or sore throat; and to have an increased prevalence of respiratory symptoms consistent with work-related asthma, compared to workers exposed to mineral oil metal-working fluids. These findings were found in individuals who currently smoked, had never smoked or were ex-cigarette smokers. Further research to determine the chemical components or microbial contaminants responsible for these findings is needed.