Zolpidem, a nonbenzodiazepine hypnotic, was identified in the blood of 29 subjects arrested for impaired driving. Zolpidem concentrations ranged from 0.05 to 1.4 mg/L (mean 0.29 mg/L, median 0.19 mg/L). In the subjects for whom zolpidem was present with other drugs and/or alcohol, symptoms reported were generally those of CNS depression. Symptoms included slow movements and reactions, slow and slurred speech, poor coordination, lack of balance, flaccid muscle tone, and horizontal and vertical gaze nystagmus. In five separate cases, where zolpidem was the only drug detected (0.08-1.40 mg/L, mean 0.65 mg/L, median 0.47 mg/L), signs of impairment included slow and slurred speech, slow reflexes, disorientation, lack of balance and coordination, and "blacking out." Although no quantitative relationship between blood concentrations and degree of driving impairment is currently possible, it is reasonable to conclude that because of its specific activity as a sleep inducer, blood concentrations consistent with therapeutic doses of zolpidem have the potential to affect driving in a negative way. Concentrations above the normal therapeutic range would further impair a person's level of consciousness and driving ability. 1 table, 2 figures, and 19 references