The assessment of potential “breakthrough infections” in HIV vaccine trials requires knowledge of viral load in unvaccinated persons. Therefore, HIV-1 RNA was quantitated in plasma from Thai adults with subtype E infections. RNA was detectable (≥500 copies/ml) in 93% of 255 specimens, with a mean (standard deviation) value of 4.09 (0.88) log copies/ml. The concentration of RNA was directly related to the presence of AIDS-defining illnesses, inversely related to CD4 count, and independent of gender after adjustment for CD4 count.