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In tests for metabolism and pharmacokinetics chlorodifluoromethane was evaluated in groups of 3 male humans exposed via inhalation to vapor concentrations of 92 or 518 ppm for 4 hours in an inhalation chamber. The compound was absorbed very quickly, reaching plateaus of 0.25 and 1.36 ug/ml after approximately 4 and 3 hours of exposure for the low- and high-dose levels, respectively. End-tidal breath concentrations of the test compound during exposure were similar to the exposure concentrations, indicating that only a small proportion of the available dose was absorbed. Elimination of the compound from blood was triphasic, with estimated half-lives of 0.005, 0.20, and 2.7 hours. The first phase probably corresponded to elimination from blood and rapidly perfused tissues, whereas the second and third phases of elimination probably corresponded to elimination from slowly perfused tissues and fat, respectively. The parent compound was detected in urine samples from all subjects; very little fluoride ion was detected in urine samples, indicating that the test compound was probably not metabolized to a significant extent.