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According to the theoretical pharmacokinetical considerations put forward by Wehner et al. the BAC ven/BrAC conversion factor Q is not a constant value and varies depending on the pharmacokinetic phase deduced from the alcohol concentration curve. Based on these considerations we propose that Q must be inversely proportional to the BrAC during the postabsorptive linear elimination phase, expressed as the hyperbola Q=1/?+(CT)/BrAC. The constants ? or 1/? and (CT)?where (CT) consists of different parameters which remain constant during the linear elimination phase?can be experimentally determined from the linear relationship BrAC=?BAC ven-?(CT). To test this hypothesis 12 human volunteers received parenteral doses of ethanol. During the elimination phase, BAC and BrAC of each volunteer were measured between 18 and 34 times in a BrAC range between 0.65 mg/l and 0.12 mg/l. The conversion factor Q was either expressed in the form of the hyperbola Q=1/?+(CT)/BrAC or directly calculated from the ratio BAC ven/BrAC and the results obtained using both methods were found to be very similar. The values of 1/? of the hyperbolic functions varied between 1.808 and 2.165 and those of (CT) between 0.004 and 0.127. For a BrAC of 0.25 mg/l, an average value of 2.308±0.080 could be calculated for the conversion factor Q 0.25. On average, the value of Q 0.40 amounted to 2.207±0.048 and that of Q 0.55 to 2.160±0.056. [ABSTRACT FROM AUTHOR]