This study indicates that the gonococcal strains of lipopolysaccharide group (II) most frequently isolated from localized infections have a growth advantage over strains of group I. Their increased association with neutrophil polymorphs and their susceptibility to lysis by normal human serum would seem to act to the disadvantage of the bacteria. Our findings taken together with the cytotoxic effect of gonococci on neutrophil polymorphs offer an explanation for this apparent paradox.