The Th1–Th2 balance plays a pivotal role in determining the outcome of an immune response to an infectious organism. It is proposed that during HIV infection, disease progression is characterized by a loss of Th1 activity, a shift to a more ‘allergic’ Th2-type response and hence loss of cytotoxic cell activity against infected host cells. This study was undertaken to investigate this balance in three groups of individuals: HIV-negative volunteers (n=10), a group of HIV-infected patients on no therapy (n=10) as well as a group of patients managed with a mixture of plant sterols/sterolins (n=9). In parallel, their response to mitogens and the subsequent expression of the activation antigen CD69 was measured. This study was conducted by three-colour flow cytometry in order to obviate the less sensitive cytokine secretion assays that have yielded controversial results. The results indicate that HIV-infected patients on no therapy exhibit a pre-dominant Th2 response (IL-4 secretion), whereas those on the sterol/sterolin mixture exhibit a beneficial Th1 response (IFN-γ). Surprisingly, in both patient groups, the expression of CD69 was abnormally low when compared to the uninfected volunteers, implying that chronic activation is already present in vivo. It appears that the detrimental Th2 driven response might be swung to the more beneficial Th1 response with the immune modulatory sterols/sterolin mixture. Clinical use of this mixture in HIV infection has yielded results which corroborate the above observations in that patients using the plant sterol/sterolin mixture maintain their CD4 cell numbers over an extended period of time in the absence of any anti-retroviral therapy.