The aim of this study was to investigate the possible influence of the tumor necrosis factor alpha (TNFA) gene promoter polymorphisms and HLA class II genes on the susceptibility to or development of human brucellosis. TNFA genotypes (at positions -308 and -238) were determined in 59 patients with brucellosis and 160 healthy controls by polymerase chain reaction-restriction fragment length polymorphism. There were no significant differences between the patients and the controls for the TNFA-238 genotypes. However, when the overall TNFA-308 genotype distribution of the brucella patients was compared with that of the control subjects, a significant skewing was observed (P = 0.02). The TNFA-308.1/2 genotype was present at significantly higher frequency in the total patient as a whole compared with control subjects (30% versus 15%; P = 0.01, odds ratio (OR) 2.49, 95% confidence interval (CI) 1.16-5.33). No statistically significant differences in the distribution of HLA-DRB1 or DQB1 alleles were observed between brucella patients and control subjects. Stratification to correct for interdependence of TNFA-308.2 and HLA-DR3 alleles confirmed that, in spite of their strong linkage disequilibrium, the association of TNFA-308.2 with brucellosis was independent of HLA-DR3.