The Zambia Emory HIV Research Project (ZEHRP) was established in Lusaka in 1994 to provide voluntary HIV-1 testing and counseling, long-term monitoring, and health care to cohabiting heterosexual couples. Details of the cohort have been described elsewhere [43] . Briefly, HIV-discordant couples enrolled in studies of transmission are monitored for seroconversion of the negative partner at three-month intervals, at which time the participants also receive preventative counseling and condoms. Banked plasma samples from seronegative partners are tested for p24 antigen by ELISA to identify individuals with acute infection [38] . The two subtype C infected seroconvertors studied here were participants in this cohort and were identified as p24 antigen positive and seropositive by rapid test and western blot, as described in [38, 44] . Plasma viral loads were determined using the Roche Amplicor HIV-1 assay. None of the subjects received antiretroviral therapy during the evaluation period.