We have identified three polymorphic microsatellites (which we call TNFa, TNFb, and TNFc) within a 12-kilobase region of the human major histocompatibility complex (MHC) that includes the tumor necrosis factor (TNF) locus. TNFc is located within the first intron of the TNF-beta gene and has only 2 alleles. TNFa and TNFb are 3.5 kilobases upstream (telomeric) of the TNF-beta gene and have at least 13 and 7 alleles, respectively. TNFa, -b, and -c alleles are in linkage disequilibrium with alleles at other loci within the MHC, including class I, class II, and class III. TNFa, -b, and -c alleles are also associated with extended HLA haplotypes. These TNF polymorphisms will allow a thorough genetic analysis of the involvement of TNF in MHC-linked pathologies.