Since 1992, cohort study of prevaience of HIV infection and incidence rate among drug users has been conducted annually at the study spots along southwestern border areas of Ruili, Longchuan and Luxi counties, Yunnan province of China. From 1992 to 1995, 859, 437, 343 and 540 drug users with a total number of 2179 cases were studied respectively. The proportion of IDUs among drug users was about 30% in 1992, and went up to about 50% in 1995. HIV serloprevalence rates among IDUs in Ruili was comparatively high. From 1992 to 1995, the rates were 81.8%, 85.7%, 61.8% and 51.9% respectively. Longchuan county was at medium, 44.6%, 40.0%, 42.2% and 43.5% respectively. Luxi kept at a lower level, which were 5.1%, 0%, 0% and 3.1%. From 1992 to 1995, the increase of incidence rates were 30.1% from 21.7% to 42.1% in Ruili county, 17.2% (12.1% to 25.9%) in Long Chuan, and 0.6% (0% to 2.3%) in Luxi. The sero-prevalence rate among the spouses of these HIV infected persons was 3.1% in 1990, but increased to 9.8%, 7.4%, 0% and 10.3% respectively from 1992 to 1995 and was 12.3% in 1997. CD4 counting was conducted in 107 cases. The result indicated at the earlier of the year being infected. The higher proportion of CD4 count which was < 500/mm3 on NASBA was applied to analyse the viral load, 3 out of 29 cases were < 1,000 copies/ml, while Log mean of viral load in 26 cases was 4.37.