The objective of this study was to assess individual human exposure to volatile halogenated hydrocarbons (VHH) under normal environmental conditions by means of biological monitoring, i.e. by the measurement of these compounds or their metabolites in body fluids, such as blood, serum, and urine. Blood samples of 39 normal subjects without known occupational exposure to these agents were examined for the occurrence of VHH. The following compounds were present in quantifiable concentrations in 60 to 95% of the blood samples examined: chloroform (median 0.2 microgram/l; range less than 0.1-1.7 microgram/l), 1,1,1-trichloroethane (median 0.2 microgram/l; range less than 0.1-3.4 micrograms/l), tetrachloroethylene (median 0.4 microgram/l; range less than 0.1-3.7 micrograms/l). Trichloroethylene could be detected in 31% of all blood samples (median less than 0.1 microgram/l; range less than 0.1-1.3 microgram/l). In addition, the levels of trichloroacetic acid (TCA) were determined in serum and 24-h urine samples of 43 and 94, respectively, normal subjects. TCA was present in measurable concentrations in all serum and urine samples examined. The median of the TCA levels in serum was 21.4 micrograms/l (range 4.8-221.2 micrograms/l) and in urine 6.0 micrograms/24 h (range 0.6-261.4 micrograms/24 h). The results are discussed in relation to data from the literature on human exposure to VHH from the general environment, i.e. via air, food, and water. The upper normal limits calculated from the results of this investigation can be used to detect even minor excessive exposures to VHH.