Isoprinosine and Imuthiol are non mitogenic immunomodulators active on T cell differentiation. In ARC patients, they modulate the circulating T cell receptor complex in terms of OKT4+ phenotype induction. This effect is not responsible for any expansion of the target population but for a partial inhibition of in vitro infection with LAV/HTLV III viral particles. At a clinical level, this means that these drugs may prove helpful in ARC patients when the virus has infected only a few helper cells.