The human aryl hydrocarbon receptor (AHR) is a protein for which there is little evidence of polymorphic variability of functional consequence. It has been hypothesized that potential variability in dioxin sensitivity may be due to polymorphisms in AHR-associated proteins, such as the human AHR-interacting protein (AIP). There are limited data on AIP single nucleotide polymorphisms (SNPs) with potential functional consequences. We sequenced 103 human DNA samples within the open reading frames of the AIP locus using samples from six ethnic populations to further characterize AIP SNPs. Eight exonic SNPs were identified at the AIPlocus, including three novel SNPs: T48T, L212L, and V302V. Combined with prior reports, there are now a total of 14 exonic SNPs that have been identified within AIP. Of these, six are non-synonymous and are therefore of potential functional importance, though only two of these (Q228K and A276V) were detected in the current study. The functional consequences of Q228K and A276V are unknown, although functional evidence from AIP SNPs associated with congenital pituitary tumors suggests that such amino acid changes are likely to have no effect or to decrease, rather than increase, sensitivity to dioxins. To date, no non-synonymous SNPs have been detected in the AHR-binding region of AIP.