The present study was designed to characterize nicotine withdrawal during a 5-day period in which smokers who were not trying to quit were offered monetary incentives to abstain while residing in their usual environments. Participants were randomly assigned to one of three groups. In two groups, monetary payment was delivered contingent on breath carbon monoxide levels (CO< or =8 ppm) indicating recent smoking abstinence, with the amount of payment differing between the two groups. The third group was a control group in which payment was delivered independent of smoking status. Participants provided CO samples three times per day (morning, afternoon- and evening) for 5 days (Monday-Friday). At each evening visit, all participants completed a nicotine withdrawal questionnaire and other questionnaires. Contingent payment significantly decreased expired-air CO and salivary cotinine levels as compared with the control group. No significant differences in abstinence were noted as a function of the amount paid. Participants in both contingent payment groups reported significantly more withdrawal symptoms than those in the noncontingent control group, including increases in anxiety and nervousness, impatience and restlessness, hunger, and desire to smoke. Such contingent payment procedures may provide an effective method for studying nicotine withdrawal in smokers that does not require the costly and inconvenient practice of housing research participants on a closed ward to prevent smoking.