Two new methods for serogrouping of meningococci, whole-cell ELISA and dot-blotting, with monoclonal antibodies against serogroups A, B, C, Y and W135 were compared with slide-agglutination applying polyclonal sera. In addition to a panel of strains with previously determined serogroups by slide-agglutination, two strain collections of meningococci were studied: 1) 50 strains isolated from patients with systemic meningococcal disease in Norway during the winter 1987-1988; 2) 133 throat strains isolated from asymptomatic carriers over the same period. For the disease strains all three methods gave identical results, whereas some carrier strains which were non-agglutinable or polyagglutinable by slide-agglutination were serogroupable by the two other methods. All the systemic strains and about half of the carrier strains were serogroupable. We find that whole-cell ELISA and dot-blotting are specific, easy to read and more sensitive compared to slide-agglutination, but the former methods are at present limited by the availability of monoclonal antibodies against only serogroups A, B, C, Y and W135.