The cause of telangiectasia was investigated in aluminum (7429905) workers. Physical examinations, biochemical tests, and hemodynamic measurements were performed on 50 current workers, 23 cases of telangiectasia, and 27 comparisons to determine the presence of metabolic disorders. Data was obtained by a self administered questionnaire and by physical examination. Medical records of 50 workers with telangiectasia were compared with those from workers with no lesions. Biopsies were conducted on lesions. Cases and comparisons were compared on the basis of social habits, history of illness, and periodic medical examination. More cases than comparisons had signs of ischemia on electrocardiograms. There were no significant differences for blood pressure, hearing loss, pulmonary function, or hemoglobin concentration. No significant differences were found in physical examinations. No liver function abnormalities were seen. Microscopic examination of the lesions showed dilatation of the capillaries, swelling of the endothelium, a ring of mononuclear cells around the vessels, slight tumescence of fibrosis of the superficial dermis, and fragmentation of the elastic fibers in the dermis. No specific ultrastructural changes were seen. Workers hired more recently had fewer telangiectasia than workers hired earlier with an equal number of years exposure. The difference was attributed to improvement of air quality in work rooms and to mandatory wearing of protective masks by workers in contact with reactors. The authors conclude that fluorides contribute to the development of telangiectasia, because the occupations in which the lesions are prevalent involve significant exposure to fluorides. There are indications that fluoride (16984488) is not the only causative agent. The high prevalence of ischemic heart disease in males with telangiectasia should not be ignored.