Individuals experiencing a primary infection with HIV (PHI) are known to undergo a potent activation of their humoral and cellular immune response. We investigated the expression of CD30 in peripheral blood mononuclear cells (PBMC) from 15 PHI patients before their initiation of HAART, since elevated levels of its soluble form, sCD30, have been previously documented in the plasma/sera of PHI patients. We also analyzed other lymphocyte-associated activation markers, including CD69, CD25 and HLA-DR. When looking at total lymphocytes, HLA-DR was expressed on the majority of lymphocytes, followed evenly by CD69 and CD25, and last by CD30. Of note, we observed that 13 out of these 15 patients displayed a characteristic expansion of lymphocytes with larger morphology (termed blasts). When a morphologic gate was drawn on these blasts, the percentage of CD25-, CD69-positive cells remained substantially unchanged, that of HLA-DR-positive cells augmented, but the the most striking increase occurred in the percentage of CD30-expressing lymphocytes. Therefore, although all of the molecules studied are considered lymphocyte activation markers, CD30 is most likely to be expressed within cycling/proliferating cells of the lymphoblast fraction during the earliest phases of HIV infection.