“…Earlier experiments have shown that the ribosomal preparations were contaminated with cell surface material (8,12,13,24,31). Although some investigators presume that the protective t Present address: National Institute of Child Health and Human Development, Bethesda, MD 20014. antigen of Salmonella must be a cell surface component, several investigators have shown that both subcellular or ribosomal fractions (8,12,18,30,42,49) and protein extracts from whole cells (3)(4)(5)(6)(7) can protect mice against a lethal Salmonella challenge. This study was undertaken to examine cell surface antigens for their protective ability and any possible association with the protective ribosomal fraction.…”