Juan Manuel Reséndiz-Hernández,1 Enrique Ambrocio-Ortiz,1 Gloria Pérez-Rubio,1 Luis Alberto López-Flores,1 Edgar Abarca-Rojano,2 Gandhi Fernando Pavón-Romero,3 Fernando Flores-Trujillo,4 Rafael de Jesús Hernández-Zenteno,4 Ángel Camarena,1 Martha Pérez-Rodríguez,5 Ana María Salazar,6 Alejandra Ramírez-Venegas,4 Ramcés Falfán-Valencia1 1HLA Laboratory, Instituto Nacional de Enfermedades Respiratorias Ismael Cosío Villegas, Mexico City, Mexico; 2Research and Graduate Studies Section, Escuela Superior de Medicina, Instituto Politécnico Nacional, Mexico City, Mexico; 3Department of Allergy and Clinical Immunology, Instituto Nacional de Enfermedades Respiratorias Ismael Cosío Villegas, Mexico City, Mexico; 4Tobacco Smoking and COPD Research Department, Instituto Nacional de Enfermedades Respiratorias Ismael Cosío Villegas, Mexico City, Mexico; 5Unit of Medical Research in Immunology, CMN S-XXI, Instituto Mexicano del Seguro Social, Mexico City, Mexico; 6Department of Genomic Medicine and Environmental Toxicology, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Mexico City, Mexico Background: Smoking and smoke from biomass burning (BB) are the main environmental risk factors for COPD. Clinical differences have been described between COPD related to smoking and related to wood smoke, but no studies have shown genetic differences between patients exposed to these two risk factors. Methods: To investigate a possible association of tumor necrosis factor (TNF) promoter polymorphisms, we conducted a case–control study. A total of 1,322 subjects were included in four groups: patients with a diagnosis of COPD secondary to smoking (COPD-S, n=384), patients with COPD secondary to biomass burning (COPD-BB, n=168), smokers without COPD (SWOC, n=674), and biomass burning-exposed subjects (BBES n=96). Additionally, a group of 950 Mexican mestizos (MMs) was included as a population control. Three single nucleotide polymorphisms (SNPs) were selected in the TNF gene (rs1800629, rs361525, and rs1800750) and one SNP in the lymphotoxin alpha gene (rs909253). Results: Statistically significant differences were found with genotype GA of the rs1800629: COPD-S vs SWOC, (p