The NcoI RFLP of the tumor necrosis factor (TNF) β gene was analyzed in a panel of f 105 unrelated healthy Italian blood donors. The gene frequencies of the f 0.5 kb and 5.5 kb allele were 0.73 and 0.27, respectively. The 5.5 kb band was significantly positively associated with HLA-A1, B8, DRI7.1, and C4AQ0, and negatively associated with DR7.2, DQw9 and C4A6, all being specificities which belong to two well-known Caucasoid ancestral haplotypes. When the population was subdivided on the basis of TNF phenotypes, different linkage disequilibria between HLA alleles were detected in the three phenotypic classes. From this analysis it was possible to relate preferential HLA associations, most of which are characteristic of ancestral haplotypes, to TNF polymorphism.