The individual fluoride exposure and the corresponding body fluid levels were studied in 41 workers in an aluminium plant in Sweden. During the shift ( 8 h) personal air samplings were performed and plasma fluoride levels determined Pre and post-shift urine fluoride excretion were also measured The average total fluoride exposure was 0 91 mg/m 3 of which 34 % was gaseous fluoride (mean value 0 31 mg/m 3 ) The mean fluoride plasma level before the shift was 23 ng/ml ( 1 2 g IM/1) and increased on average to 48 ng/ml (range 14-151 ng/ml) at the end of the shift The plasma levels found were in no case remarkably high There was a high correlation between fluoride renal clearance and urinary flow (r = 0 481 ; N = 38 ; P = 0.00232) A high fluid intake during the shift will thus increase the capacity of the kidney to excrete fluoride and decrease the levels of fluoride in the body There was a significant correlation between the amount of gaseous fluoride and the area under the plasma concentration-time curve (r = 0 459 ; n = 40 ; P = 0 0029) and also the amount of fluoride excreted (r = 0 530 ; n = 40 ; P = 0 0004) When fluoride exposure and body burden are to be studied on an individual basis these two parameters give better quantitative information and are to be recommended instead of urine fluoride concentration measurements The prevention of fluoride inhalation by using a safetymask during the shift was also demonstrated The workers who used a safety-mask during the whole shift reduced the inhalation of fluoride to 30 to 40 % compared to those who did not use any mask.