Blood–air and tissue–blood coefficients (λ) are essential to characterize the uptake and disposition of volatile substances, e.g. by physiologically based pharmacokinetic (PBPK) modelling. Highly volatile chemicals, including many hydrofluorocarbons (HFC) have low solubility in liquid media. These characteristics pose challenges for determining λ values. A modified head-space vial equilibrium method was used to determine λ values for five widely used HFCs. The method is based on automated head-space gas chromatography and injection of equal amount of chemical in two head-space vials with identical air phase volumes but different volumes of the liquid phase. The liquids used were water (physiological saline), fresh human blood, and olive oil. The average λ values (n = 8) were as follows: 1,1-difluoroethane (HFC152a) – 1.08 (blood–air), 1.11 (water–air) and 5.6 (oil–air); 1,1,1-trifluoroethane (HFC143a) – 0.15, 0.15 and 1.90; 1,1,1,2-tetrafluoroethane (HFC134a) – 0.36, 0.35 and 3.5; 1,1,1,2,2-pentafluoroethane (HFC125) – 0.083, 0.074 and 1.71; and 1,1,1,3,3-pentafluoropropane (HFC245fa) – 0.62, 0.58 and 12.1. The λ values appeared to be concentration-independent in the investigated range (2–200 ppm). In spite of the low λ values, the method errors were modest, with coefficients of variation of 9, 11 and 10% for water, blood and oil, respectively. Copyright © 2009 John Wiley & Sons, Ltd.