For smoking cessation, several treatment modalities already exist, and some individuals manage to stop smoking on their own. The study by Chen et al. (2) focuses on a candidate region that has been the subject of a growing literature (9, 10). Three nicotinic receptor subunits are on an adjacent segment of the 15th chromosome, and there are three common haplotypes in this area that were defined using two polymorphic nucleotides (GC, GT, and AC). Genetic polymorphisms are often in linkage equilibrium with other polymorphisms (i.e., when one allele is inherited, so is the linked allele), and co-inherited blocks of a chromosome are defined as haplotypes.