Normal spleen cells from high IgE responder, BDF1 mice, formed IgE-potentiating factor upon incubation with mouse IgE, whereas those from low IgE responder, SJL mice, formed IgE-suppressive factor. The majority of the factors from BDF1 spleen cells had affinity for lentil lectin; those from SJL mice lacked affinity for the lectin. BDF1 spleen cells could be switched, however, to form IgE-suppressive factor if the cells were incubated with IgE in the presence of lipomodulin , a phospholipase inhibitory protein. In contrast, SJL spleen cells could form IgE-potentiating factor in the presence of lysolecithin, which enhances the glycosylation of IgE-binding factors. When the two strains were primed with alum-absorbed ovalbumin and their spleen cells were stimulated with homologous antigen, IgE-binding factors were detected in culture filtrates. The factors formed by BDF1 spleen cells selectively potentiated the IgE response, however, whereas those formed by SJL spleen cells selectively suppressed the response. Analysis of the cellular mechanisms for the selective formation of IgE-potentiating factor by antigen-primed BDF1 spleen cells revealed that antigenic stimulation of Lyt-1+ T cells resulted in the formation of two T cell factors, i.e., an "inducer" of IgE-binding factor and a glycosylation-enhancing factor, and that these factors induced the selective formation of IgE-potentiating factor. In SJL spleen cells, antigenic stimulation of Lyt-1+ T cells resulted in the formation of an "inducer" and a glycosylation-inhibiting factor, and those factors in turn stimulated the formation of IgE-suppressive factor. An additional difference between the two strains was found in Fc gamma R+ Ly-1+ T cells that were the cell source of IgE-binding factors. Upon stimulation with IgE or "inducer", BDF1 Lyt 1+ cells formed IgE-potentiating factor, whereas the same subset of T cells from SJL mice formed IgE-suppressive factor. The results indicate that the genetic differences between the two strains with respect to the nature of IgE-binding factors appear to be expressed in the process of glycosylation of IgE-binding factors.