OBJECTIVE: Search for the rate of HIV-1 contamination among seronegative sexual partners of seropositive individuals. METHODS: Classical serological methods (EIA, WB) and PCR. SERIES: 36 heterosexual couples from central Africa, accounting for a total of 73 persons: 13/37 seropositive women, 23/36 seropositive men. All couples were serologically discordant, i.e. one partner was seropositive. CONCLUSIONS: In such a population, particularly at risk of HIV contamination, the rate of false negative serological diagnosis reached 70%