Nicotine chewing gum is designed to maintain plasma nicotine levels during a smoking cessation effort while the individual copes with the loss of the repetitive behavioral components of smoking. The plasma nicotine levels obtained with hourly gum chewing were compared with levels obtained with cigarette smoking in nine patients with lung disease. Chewing 2- and 4-mg nicotine gum hourly produced mean steady-state plasma nicotine levels of 11.8 and 23.2 ng/mL, respectively. This compares with a mean plasma nicotine trough level during usual smoking of 15.7 ng/mL and a mean trough level of 18.3 ng/mL with hourly smoking of a cigarette with a nicotine yield of 1.1 mg. Few side effects were seen with the use of either the 2- or 4-mg gum. In a short-term study, nicotine gum proved an acceptable source of nicotine for aiding smoking cessation.