Besides nicotine, other chemicals in tobacco smoke, such as norharman, may contribute to the addictive properties of cigarettes. More specifically, elevated blood plasma levels of norharman may reduce feelings of craving among tobacco-dependent individuals. To test this hypothesis, plasma concentrations of norharman were measured in 38 male smokers (at least 15 cigarettes per day) at three time-points on 3 different days spread over a 4-month period. The first measurement (T0) was conducted in the morning at 8.30 a.m., after 12 hours of smoking abstinence. The T1 and T2 measurements were conducted at 13.00 p.m. and 16.30 p.m., during a period of ad libitum smoking (after the T0 measurement, participants were not restricted in their smoking behaviour). At each of the nine time-points, craving was assessed by means of a shortened version of the Questionnaire of Smoking Urges. The Fagerström Test of Nicotine Dependence was used to obtain an indication of nicotine dependence. The results showed that, after a period of smoking abstinence, craving was stronger in those with a high tobacco dependence than in those with a low tobacco dependence. After resumption of smoking, craving declined to a similar low level in both low and high dependent smokers. Measurements during periods of ad libitum smoking indicate that plasma levels of norharman are related negatively to craving among low nicotine-dependent smokers, but not among high dependent smokers.