An increasing number of heroin and ecstasy seizures were recorded by the Norwegian police and customs authorities in the 1990s. The number of apprehended drivers in whom heroin and ecstasy were detected also rose in the same period (Heroin, 1991: n = 17, 1999: n = 320. Ecstasy, 1995: n = 6, 1999: n = 123). Drivers who tested positive for heroin (detected in urine as the metabolite 6-monoacetyl-morphine, 6-MAM) or ecstasy (3,4-methylenedioxy-metamphetamine, MDMA, detected in blood) were characterized with regard to age distribution, drug use pattern, and earlier arrests. In 1998-1999, the police apprehended 9013 drivers on suspicion of being under the influence of drugs other than alcohol. Blood and urine samples from the drivers were sent to the Norwegian Institute of Public Health, Division of Forensic Toxicology and Drug Abuse and analyzed for the most commonly abused drugs. 6-MAM was detected in urine in 7% of the cases (n = 637), representing 542 different drivers (male: 85%, n = 463, female: 15%, n = 79) as some drivers were rearrested several times during the selection period. MDMA was detected in 2% of the cases (n = 190), representing 177 drivers (male: 90%, n = 160, female: 10%, n = 17). The median ages of drivers who tested positive for 6-MAM or MDMA were 32 and 24 years, respectively. Multi-drug use was very common in both groups (83% and 98% for the heroin and ecstasy group, respectively). Drivers in both groups were followed back to 1985 to detect earlier arrests for the same offence. Of the heroin group, 78% (n = 417) had earlier been arrested for drunken or drugged driving. Alcohol was the drug most frequently detected on first arrest. Of the ecstasy group, 47% (n = 83) had earlier been arrested, and amphetamine was most frequently found on first arrest.