Multilamellar, "fluid" liposomes containing an appropriate concentration of a synthetic dinitrophenylated lipid hapten behave as T-independent (TI), adherent cell-dependent antigens for primary, in vitro, stimulation of hapten-specific IgM plaque-forming cells (PFC). The appropriate concentration of hapten is approximately 1 mol% with respect to the other liposomal lipids, cholesterol, and dimyristoylphosphatidylcholine (DMPC). At a higher hapten concentration, 4 mol%, liposomes will suppress the anti-dinitrophenyl PFC response to co-cultured immunogenic liposomes, but not the anti-sheep cell response to co-cultured sheep cells. This suppression is also TI. The ability of "fluid," haptenated liposomes specifically to stimulate or to suppress the TI PFC response is determined by the ratio of hapten to other lipids in a manner that is independent of the total hapten concentration in culture.