Preliminary findings of a NIOSH evaluation of occupational exposure of automobile production workers to metalworking fluids (MWF) were presented. The evaluation was requested following the diagnosis of six biopsy confirmed cases of hypersensitivity pneumonitis (HP) among workers at three southeastern Michigan manufacturing facilities. A case report of one worker, including clinical symptoms, work history, pulmonary function tests, and treatment was presented. Four cases of HP were reported during 1994 to 1995 by health clinics. The two subsequent cases were discovered during a review of worker medical records. An additional 14 probable cases of HP were identified but not confirmed by biopsy. Of the six confirmed HP cases, all were nonsmokers and all but one associated symptoms with working in areas with MWF exposure. Job descriptions for the afflicted workers were toolmaker, machining supervisor, grinder, metal machine repair, machinist and carpenter. Work related symptoms, initial pulmonary function tests and biopsy results were reported. Pulmonary function improved in all six workers following their removal from MWF exposure. Serum precipitin tests were negative in both workers tested. An editorial note qualified the presented findings on the basis of four limitations. It was pointed out that the cases of HP were not systematically identified, that MWF exposure was not measured, that HP prevalences and incidences were not estimated, and that no precipitating antibodies were found in the tested workers. The editors conclude that improved surveillance of workers exposed to MWF is necessary to ascertain the association of MWF to HP.