GGT and blood alcohol concentration (BAC) were measured of 2,655 male car drivers using alcoholized their cars during the year 1991 in the area of the city of Cologne. The results were evaluated statistically together with other parameters like age, time of taking blood sample and behaviour while drunken. BAC was 1.6% and more in 30.5% of all cases. Half of them had levels of 2.0% and higher. GGT in serum was increased (> 28 U/l) at 29.5% of the drivers, in 6% even above 100 U/l. 53% were younger than 31 years. Medium BAC and part of GGT higher than 28 U/l were remarkable lower in this group than at the older ones. 50% of all car drivers with blood alcohol levels above 2.0% have alcohol problems regarding GGT. Problem drinkers were found among the younger ones to an extent of 15%, but of 50% among the drivers older than 40 years. But also 25% of all with a BAC lower than 1.6% showed increased GGT levels. They remain undetected on account of the present instructions of MPA though there is a great danger repeating drunken driving. On the other side nearly 50% of those driving with an BAC of 1.6% or more are no driving drinkers regarding GGT but have to undergo MPA. The recommendation of the 30. German Traffic Courts Meeting in 1992 to determine other indicators of alcohol habituation in the blood samples taken after drunken driving like GGT and methanol should be taken in a corrected setting of the instructions. This would regard fairer the problems of an individual case. The connection of MPA with the height of BAC and other circumstances seen as indicators for extraordinary alcohol habituation is a wrong way and unnecessary if alcoholism markers are used like GGT, CDT and methanol.