A lowering of thresholds in blood alcohol determination can be realized by critical reflection on efficiency of the techniques of measurement including calibration and internal and external quality control. A threshold value can be controlled by a technique of measurement if the prognosis interval of this technique is equal or smaller than the control interval. From date 1/7/1990 we measure blood probes like described. Blood measurement before this date must be proofed for accuracy. In cases of non compliance the old threshold value should be used.