2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a powerful toxicant that exerts its effects through the aryl hydrocarbon receptor (AHR) governed by the Ahr locus that in mice is located on chromosome 12. We used single marker analyses of the offspring of female mice treated/not treated with TCDD to search for a gene (quantitative trait locus or QTL) on chromosome 12 near the site of the Ahr locus to test whether this locus appeared to affect mandible size, shape, and/or asymmetry especially in the treated mice. These mice were sampled from the F(2) generation of an original intercross of two strains (C57BL/6J and AKR/J) known to be divergent in their response to TCDD. A QTL affecting mandible shape was found on chromosome 12, but its effect on mice in the treated and control groups did not differ and it was concluded that this QTL probably was not the Ahr locus itself. We also probed a second chromosome (11) and found a QTL whose effects on asymmetry of mandible shape differed in the two environments. These results suggested that the entire genome in these mice should be scanned to search for additional QTLs that might be affected by TCDD to learn more about the potential effects of this powerful toxicant on these genes.