Restoration of IgG antibody binding to heat-denatured meningococcal outer membrane proteins has been studied on immunoblots with a series of 14 detergents. Nitrocellulose strips with the blotted proteins were incubated with the detergents and sera from human volunteers vaccinated with meningococcal membrane proteins. Zwitterionic and ionic detergents, containing substituted quarternary ammonium or amino groups with a minimum of 10 C atoms in the alkyl chain, restored the antigenicity of the serotype-specific class 2 porin protein. The concentrations of the Zwittergent detergents necessary for activation decreased with increasing alkyl chain length of the homologues. Only zwitterionic detergents renatured the class 1 protein. Both proteins were weakly antigenic in the presence of the nonionic detergents Triton X-100 and Tween 20. Meningococcal lipopolysaccharide restored antibody binding to the porin, but not to the class 1 protein. Similar concentrations of lipopolysaccharides from two other gram-negative bacteria had no effect.