This study was conducted to evaluate the health hazards and to develop diagnostic methods of glass fiber workers. We examined 40 male glass fiber workers (exposure group) and 57 male non-glass fiber workers (reference group) with a questionnaire, physical examination, chest x-ray and pathological examination in Mar, 1997. Also we examined 65 male glass fiber workers (exposure group) and 42 male non-glass fiber workers (reference group) with the same methods also we did some energy-dispersive x-ray analyses with a scanning electron microscopic examination in Sep. 1997. Most of the clinical symptoms were significantly more frequent among the exposure group than the reference group. Coughing (32.5%), itching of the nose (30.0%), irritation of eyes (27.5%), irritation of the nose (25.0%) and sputum (22.5%) were the major symptoms among the exposure group in Mar. 1997. Only itching of the nose was significantly more frequent in Sep. 1997. No cases of pneumoconiosis were observed among the groups and there were no differences in chest abnormalities between the exposure group with the reference group on both examinations. The prevalence of dermatosis among the exposure group was 20.0% (8 cases) and the cumulative prevalence was 72.5% (29 cases) in Mar. 1997. The prevalence of dermatosis among the exposure group was 23.1% (15 cases) and the cumulative prevalence was 58.5% (38 cases) in Sep. 1997. Onset of dermatosis among the exposure group was most frequent within one month after handling. The frequent sites of skin lesions were the hands and arms on both examinations. Glass fiber induced skin lesions can be diagnosed by the scotch tape method or KOH mount and then can be examined under the light, polarizing and phase-contrast microcopies. Glass fibers can be identified by some energy-dispersive x-ray analyses with a scanning electron microscopic examination.