The impact of occupational exposure to jet fuel on antipyrine elimination was studied in 91 fuel-filing attendants. The mean antipyrine clearance was enhanced to 68.4 (SD 19.5) ml/min during exposure to jet fuel compared to 57.9 (SD 18.1) ml/min after an exposure-free period of two to four weeks. The corresponding values for 47 office workers (referents) were 62.7 (SD 22.2) ml/min and 56.4 (SD 22.3) ml/min. The median jet fuel concentration in the breathing zone of the fuel-filling attendants was 31 (range 1-1 020) mg/m3. No known inducing factor could be identified in the work environment of the office workers. No difference in the concentration of aspartate aminotransferase and alkaline phosphatase in serum was found either within or between the groups. Our study indicates that jet fuel, which is a mixture of aliphatic and aromatic organic solvents resembling gasoline and white spirit, is an inducer of hepatic drug metabolism in man.