Eight immunotype lipopolysaccharides (LPSs) of Neisseria meningitidis were prepared by the phenol-water procedure and characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and sugar analyses. By SDS-PAGE and a highly sensitive silver strain. N. meningitidis LPSs from cells grown in tryptic soy broth were shown to contain one or two predominant components and a few minor, somewhat higher-molecular-weight components. The molecular sizes of the two predominant components were approximately the same as those of two E. coli rough-type LPSs, one with a complete core and the other with an incomplete core. The molecular weight of the major LPS component varied somewhat among different immunotypes but was estimated to be in the range of 4,200 to 5,000. By sugar analyses, the eight immunotype LPSs were different in their monosaccharide compositions. All contained glucose, galactose, heptose, glucosamine, and 2-keto-3-deoxyoctonate, but in different molar ratios. The growth of N. meningitidis in tryptic soy broth under different levels of aeration resulted in a change in the two major LPS components seen on the SDS-PAGE gel. High aeration increased the amount of the smaller component, whereas low aeration increased the amount of the larger component. Sugar analyses of LPSs from high and low aeration indicated that the larger LPS component contained more galactose residues per molecule. Use of different media for cell growth may also result in small, but noticeable, variations in the LPS components and in the galactose content of the LPS. The observed heterogeneity of N. meningitidis LPS may explain why many strains of N. meningitidis appear to possess more than one immunotype.