In about 50％ of the patients infected with subtype B HIV-1, the emergence of an HIV-1 using CXCR4 as co-receptor (X4-or dual-usage) seems to be associated with accelerated disease progression.It is not known whether such an association occurs with other HIV-1 subtypes.In this study, we used specimens from 473 treatment-na? ve patients enrolled in a Chinese cohort study (National Key Technologies R&D Program for the 11 th Five-year Plan) to analyze the prevalence of subtypes and co-receptor usage.No injecting-drug users were included in the cohort.Almost three quarters of participants were male; the median age was 36 (range: 18-65).Sexual contact comprised 76.7％ ; 44.8％ were men who have sex with men.Blood transfusion accounted for 9.3％ of infection, and 14.0％ were not accounted for.The CD4 + T cell counts of the participants were less than 350cells/μl.We used nucleotide sequences of V3 region of the envelope gene (from directly sequencing RT-PCR samples).Subtyping (from a phylogenetic tree) showed that 41.0％ of the specimens were CRF01_AE, 32.2％ were B or B; and 26.8％ were CRF07 or 08_ BC.The genotypic co-receptor usage analysis (Geno2pheno algorithm) showed that the proportion of X4 or dual usage was 63.9％ in subtype CRF01_ AE;38.3％ in B or B; and only 6.0％ in CRF07 or 08_ BC.We are now confirming our results of the genotypic predictions by our newly established method for phenotypic analysis of co-receptor usage using the Dual-Split-reporter protein system.