The murine B lymphocyte receptor for the Fc portion of IgE (FcεR) was further characterized by using the membrane impermeable cross-linking reagents 3,3′-dithiobis-(sulfosuccinimidyl) proprionate (DTSSP) and bis-(sulfosuccinimidyl) suberate (BS3). IgE could be cross-linked to the FcεR on the intact cells with either reagent and, in addition, up to 10% of the B cell surface immunoglobulin (slg; both IgM and IgD) was also found to cross-link to the IgE/FcεR complex. Analysis of isolated sIg/IgE/FceR complexes indicated that about 60% of the FcεR molecules were becoming cross-linked to slg. Thus, the data suggest that on the intact murine B cell the FcεR is frequently in close association with sIg. The murine B cell FcεR was also examined for the presence of receptor-associated proteins that are buried in the membrane. Advantage was taken of the membrane-impermeant nature of DTSSP and BS3. IgE was cross-linked to the FcεR on intact cells by using the disulfide-cleavable DTSSP and following solubilization with nonionic detergent; BS3 was used to crosslink possible internal membrane components to the FcεR. In these experiments, the high-affinity FcεR on rat basophilic leukemia (RBL) cells could be cross-linked to a nonreduceable high molecular weight complex of 100 kilodaltons. However, when intact murine B cells were treated with DTSSP, solubilized and treated with BS3 in the same manner as indicated above, no evidence was found for the presence of membrane-buried receptor-associated proteins with the B cell FcεR. Thus, these data further support the concept that there may be little relationship between the high-affinity mast cell/basophil FcεR and the low-affinity lymphocyte FcεR.