This invention is a new carrier for conjugate vaccines. The carrier is lipopolysaccharide (LPS) isolated from Brucella abortus (BA). The claims of the patent cover all conjugates comprising BA-LPS and an antigen from an infectious agent or tumor. BA-LPS, like other LPSs from gram-negative bacteria, raises antibody responses in a T-independent fashion, which allows antibodies to be raised in the absence of T cell help. BA-LPS is much less toxic than LPS from other bacteria, and is much less potent than other bacterial LPS in inducing inflammatory cytokines. Thus, BA-LPS is much less likely to cause endotoxic shock. There are no foreign patent rights. The invention is further described in Infection & Immunity 61(5), pp. 1722-1729, 1993.