Immunization of mice containing mutations that inactivate the TCR Cβ and Cδ genes with the T cell-independent (TI) type 2 Ag (4-hydroxy-3-nitrophenyl) acetyl-Ficoll induces clusters of peanut agglutinin-binding B cells in the spleen. These clusters are histologically indistinguishable from germinal centers (GCs) typical of T cell-dependent immune responses. They are located in follicles, and contain mature follicular dendritic cells, immune complex deposits, and B cells that display the phenotypic qualities of conventional GC B cells. However, the kinetics of this TI GC response differ from T cell-dependent GC responses in being rapidly induced and of short duration. Moreover, the Ab V genes expressed in TI GCs have not undergone somatic hypermutation. Therefore, T cells may be required for B cell differentiation processes associated with the intermediate and latter stages of the GC reaction, but they are dispensable for the induction and initial development of this response.