Cigarette smoking is the most preventable cause of death in the United States. In fact, the number of deaths related to tobacco is more than all deaths related to human immunodeficiency virus (HIV), illegal drug use, motor vehicle injuries, suicides, and murders combined; yet 21% of adults in the United States smoke. Approximately 90% of adult smokers first initiate tobacco use during adolescence, suggesting that nicotine initiation and nicotine dependence have a substantial age related component. In addition, there is evidence of a substantial genetic component in nicotine addiction. The following studies examine the effect of a natural occurring single nucleotide polymorphism (SNP) in the nicotinic acetylcholine receptor α4 subunit gene, Chrna4 , on nicotine related phenotypes. The SNP leads to an alanine/threonine variation in the amino acid sequence of the Chrna4 gene at amino acid position 529. Several different approaches were employed to examine the effect of the polymorphism. Chrna4 T529A knock-in mice were used to detect differences in nAChR function and expression and to directly evaluate the influence of the polymorphism on nicotine induced behaviors in adult mice. Age also was examined in Chrna4 T529A knock-in mice to determine its effects on baseline measures of anxiety and nicotine consumption, because adolescence is associated with increased sensation seeking, increased novelty seeking, and decreased anxiety. Additionally, two inbred mouse strains were used to evaluate strain and age effects in nicotine consumption and anxiety-like behaviors. The results of these studies indicated the Chrna4 T529A polymorphism had a modest effect on nAChR function and nicotine induced behaviors in adult animals. In addition, strain and genotype influenced many of the phenotypes, but in an age and sex dependent manner.