Cell membrane gangliosides have been shown to be involved in a number of biological processes including cell adhesion, signal transduction and ligand receptor interactions. In this paper we analyzed the effects of a mixture of bovine brain gangliosides, currently in clinical use, on cell mediated immune responses in vitro. We show here that exogenous gangliosides inhibit mitogen and alloantigen induced lymphoproliferation. On the other hand effects on antigen induced blastogenesis were exquisitely dose dependent in that while high doses of gangliosides inhibited lymphoproliferation, probably by interfering in interleukin 2 receptor interactions, lower doses significantly enhanced antigen induced responsiveness. We also report that gangliosides inhibit the generation of lymphokine activated killer cells. Altogether, these data underline the immunoregulatory potential and the polymorphism of effects of exogenous gangliosides.