We tested the association of MHC ancestral haplotypes with rapid or slow progression to AIDS by comparing their frequencies in the French genetics of resistance/susceptibility to immunodeficiency virus cohort with that reported in a control French population. Seven ancestral haplotypes were identified in the genetics of resistance/susceptibility to immunodeficiency virus cohort with a frequency >1%. The 8.1 (odds ratio (OR) = 3, p = 0.006), 35.1 (OR = 5.7, p = 0.001), and 44.2 (OR = 3.4, p = 0.007) ancestral haplotypes were associated with rapid progression, whereas the 35.2 (OR = 3.6, p = 0.001), 44.1 (OR = 5.4, p < 10(-4)), and 57.1 (OR = 5.8, p < 10(-4)) ancestral haplotypes were associated with slow progression to AIDS. Although the frequency of each ancestral haplotype is low in the population, the OR were quite higher than those previously obtained for single HLA allele associations, with some p values as low as 10(-4). The analysis of the recombinant fragments of these haplotypes allowed the identification of the MHC regions in the 35.1, 35.2, and 44.2 haplotypes associated with rapid progression to AIDS and the MHC regions of the 44.1 and 57.1 haplotypes associated with slow progression to AIDS. Previous studies have identified single HLA alleles associated with disease progression. Our results on recombinant fragments confirm the direct role of HLA-B35 in rapid progression. Associations with HLA-A29 and -B57 might be due to linkage disequilibrium with other causative genes within the MHC region.