Aims. To compare a transdermal nicotine patch designed for 24-hour wear with one designed for 16-hour wear for relief of craving and withdrawal, particularly in the morning hours. Design. Smokers were randomly assigned to use one of two common patch regimens: NicoDerm/NiQuitin (24-hour wear, 21 mg nicotine) or Nicotrol/Nicorette (16-hour wear, 15 mg). In a double-dummy design, participants wore two patches during the day, one active, one placebo and one patch while sleeping. Setting. A smoking cessation research clinic. Participants. Two hundred and forty-four smokers who suffered morning cravings. Intervention. Two patch formulations approved and marketed for over-the-counter use in the US- NicoDerm CQ (labeled as 21 mg over 24 hours) and Nicotrol (labeled as 15 mg over 16 hours)-were each used according to its instructions. Smokers also received behavioral counseling. Measurements. For a week of baseline and 2 weeks after quitting, smokers used palm-top computers to assess craving and withdrawal symptoms several times each day. Findings. The 21 mg/24-hour patch yielded consistently better control of craving, not only during the morning hours, but throughout the day, and over the 2-week period of abstinence. Additionally, the 21 mg/24-hour patch yielded greater reductions in anxiety, irritability and restlessness. Smokers using the 21 mg/24-hour dosing regimen also experienced longer abstinence than those using the 15 mg/16-hour patch. Conclusions. These findings demonstrate that 24-hour dosing with a 21 mg patch affords superior relief of craving and withdrawal during the first 2 weeks of abstinence, when symptoms are at their peak, and when relapse is most likely. They confirm the importance of dosing parameters in nicotine replacement products.