To determine if CFH and LOC387715/ARMS2 genotypes influence treatment response to AREDS-type nutritional supplementation with antioxidants and zinc.Retrospective analysis of participants in a randomized, controlled clinical trial, the Age-Related Eye Disease Study (AREDS).Eight hundred seventy-six AREDS study participants who were considered at high risk for developing advanced age-related macular degeneration (AMD).Using DNA extracted from venous blood of 876 white participants in AREDS categories 3 and 4, that is, those considered to be at high risk for progression to advanced AMD, the authors genotyped for the single nucleotide polymorphisms in the CFH (Y402H, rs1061170) and LOC387715/ARMS2 (A69S, rs10490924) genes. The authors performed adjusted unconditional logistic regression analysis and assessed interactions of these genotypes to determine the relationship between CFH and LOC387715/ARMS2 genotype and treatment with antioxidants plus zinc.Interaction between genetic variants and treatment response as determined by progression from high-risk to advanced AMD.Progression occurred in 264 of 876 patients from AREDS category 3 (intermediate AMD) to category 4 or 5 (unilateral or bilateral advanced AMD, respectively), or from category 4 to category 5. A treatment interaction was observed between the CFH Y402H genotype and supplementation with antioxidants plus zinc (CC; P = 0.03). An interaction (P = 0.004) was observed in the AREDS treatment groups taking zinc when compared with the groups taking no zinc, but not in groups taking antioxidants compared with those taking no antioxidants (P = 0.59). There were no significant treatment interactions observed with LOC387715/ARMS2.The findings of this study indicate that an individual's response to AREDS supplements may be related to CFH genotype. This could have clinical relevance by predicting treatment outcome and potentially preventing unwanted side effects in those who may not benefit. Corroboration of these analyses is needed before considering modification of current management. This is among the first pharmacogenetic studies to suggest interaction between genotype and treatment.