Drug and alcohol dependence are associated with enhanced attention for drug-related stimuli. This cognitive processing bias has been suggested to be related to craving and to represent one of the core mechanisms of addition. The present study tests the hypothesis that enhanced attention for heroin cues is mediated by the dopaminergic system using haloperidol as dopamine antagonist. In a double blind, randomized crossover design, 17 detoxified heroin dependent patients received a single oral dose of haloperidol 2 mg and placebo. Patients performed an Emotional Stroop Task to assess the cognitive processing of drug cues under both conditions. In addition, self-reported craving was assessed. In the haloperidol condition, patients performed better on the Emotional Stroop Task than in the placebo condition. However, no effect of haloperidol on subjective craving was found. These findings provide preliminary indications that attentional bias in heroin dependent humans is mediated by dopaminergic mechanisms.