Analytical records concerning 440 living drivers suspected of driving under the influence of drug (DUID) were collected and examined during a 2 years period ranging from 2002 to 2003 in canton de Vaud, Valais, Jura and Fribourg (Switzerland). This study included 400 men (91%) and 40 women (9%). The average age of the drivers was 28 ± 10 years (minimum 16 and maximum 81). One or more psychoactive drugs were found in 89% of blood samples. Half of cases (223 of 440, 50.7%) involved consumption of mixtures (from 2 to 6) of psychoactive drugs. The most commonly detected drugs in whole blood were cannabinoids (59%), ethanol (46%), benzodiazepines (13%), cocaine (13%), amphetamines (9%), opiates (9%) and methadone (7%). Among these 440 cases, 11-carboxy-THC (THCCOOH) was found in 59% (median 25 ng/ml (1–215 ng/ml)), Δ 9-tetrahydrocannabinol (THC) in 53% (median 3 ng/ml (1–35 ng/ml)), ethanol in 46% (median 1.19 g/kg (0.14–2.95 g/kg)), benzoylecgonine in 13% (median 250 ng/ml (29–2430 ng/ml)), free morphine in 7% (median 10 ng/ml (1–111 ng/ml)), methadone in 7% (median 110 ng/ml (27–850 ng/ml)), 3,4-methylenedioxymethamphetamine (MDMA) in 6% (median 218 ng/ml (10–2480 ng/ml)), nordiazepam in 5% (median 305 ng/ml (30–1560 ng/ml)), free codeine in 5% (median 5 ng/ml (1–13 ng/ml)), midazolam in 5% (median 44 ng/ml (20–250 ng/ml)), cocaine in 5% (median 50 ng/ml (15–560 ng/ml)), amphetamine in 4% (median 54 ng/ml (10–183 ng/ml)), diazepam in 2% (median 200 ng/ml (80–630 ng/ml)) and oxazepam in 2% (median 230 ng/ml (165–3830 ng/ml)). Other drugs, such as lorazepam, zolpidem, mirtazapine, methaqualone, were found in less than 1% of the cases.