I propose to take advantage of an unique ongoing study to explore how polymorphisms in low penetrance metabolic and DNA repair genes may modulate diet-cancer associations. The study is carried out in USA and deals with colorectal cancer (CRC) in relation to fish- and meat related mutagens exposure. For a period of one year I will be based at The University of Southern California (USC), Department of Preventive Medicine. Here I will work with prominent experts in molecular epidemiology and attend advanced classes in genetic epidemiology. I have already obtained some funding from "Henning och Johan Throne-Holsts stiftelse för främjande av vetenskaplig forskning" for this postdoc exchange. I hypothesize that single nucleotide polymorphisms (SNPs) in genes th at play key roles in the activation and/or detoxification of fish- and meat related mutagens, may modify the effects of mutagen intake on CRC risk. The Los Angeles CRC cohort consists of the USC`s component of the US Colorectal Family Registry (CFR). This registry is the largest in its kind (7,000 patients) and consists of CRC patients and their families. The large sample sizes in this study represents an excellent opportunity for the study of SNPs and gene-environment interactions. I hope to be able to r eveal associations and gene-environment interactions that could help us to understand the heterogeneity of exposure and susceptibility with respect to CRC.