The associations between a polymorphism of the serotonin transporter gene (5-HTTLPR), dental mercury exposure, and self-reported symptoms were evaluated among 157 male dentists and 84 female dental assistants. Self-reported symptoms and detailed work histories were obtained by computerized questionnaire. Spot urine samples were collected and analyzed for mercury concentrations to evaluate recent exposures, whereas a chronic mercury exposure index was created from the work histories. 5-HTTLPR polymorphism status was determined using a polymerase chain reaction (PCR)-based assay. Scores for current, recent, and chronic self-reported symptom groups were evaluated with respect to recent and chronic mercury exposure and 5-HTTLPR polymorphism status. Multiple regression analysis controlled for age, socioeconomic status, tobacco and alcohol use, self-reported health problems, and medications. Analyses were restricted to Caucasian subjects due to the highly skewed distribution of the 5-HTTLPR polymorphism. Separate evaluations were conducted for dentists and dental assistants. In contrast to previous reports, no consistent associations were found between either urinary mercury concentration or the chronic index of mercury exposure and any category of symptoms. However, both significant and consistent associations were observed between increased symptoms and the 5-HTTLPR polymorphism involving two copies of the short or "s" allele (full mutation), but not with the polymorphism involving only one copy (heterozygous), demonstrating a gene-dose relationship for symptom reporting. These findings suggest that within this restricted population increased symptoms of depression, anxiety, and memory are associated with the 5-HTTLPR polymorphism among both males and females.Historically, occupational exposures to high levels of elemental mercury (Hg 0 ) have been associated with potentially severe neurological deficits (Albers et al., 1988;Langworth et al., 1992;Pranjic et al., 2003;Piikivi et al., 1984;Piikivi & Hanninen, 1989), whereas more recent studies reported such effects at substantially lower levels of Hg 0 exposure (Clarkson et al., 2003;Langworth et al., 1997;Ngim et al., 1992;Ritchie et al., 2002;Shapiro et al., 1982;Soleo et al., 1990). Our own studies documented adverse neurobehavioral effects associated with elemental mercury exposures in the range of those experienced by the general population with mercury amalgam dental fillings Echeverria et al., 1995Echeverria et al., , 1998. At such low levels of exposure, it becomes prudent to control for individual factors that may influence the sensitivity to Hg 0 -mediated effects. To this end, our previous studies described increased susceptibility to the adverse neurobehavioral effects of Hg 0 exposure among dentists and dental assistants expressing polymorphisms of genes encoding the heme biosynthetic pathway enzyme, coproporphyrinogen oxidase (CPOX) , and brain derived neurotrophic factor (BDNF) (Heyer et al., 2004;Echeverria et al., 2005). The polymorphism in e...