A total of 103 Neisseria strains, including 42 carrier and 40 invasive N. meningitidis and 21 commensal species were studied. Outer‐membrane proteins from carrier and invasive N. meningitidis showed similar molecular mass distributions (except in the range from 78 to 82 kDa in which 90% of the invasive but only 47.6% of the carrier strains expressed proteins), many strains showin neither class II (41 kDa) nor class III (38 kDa) proteins. When grown in iron‐restricted conditions proteins were induced mainly in the ranges from 62 to 92 kDa with no significant differences between groups. Commensal species, both in normal and in iron‐restricted conditions, showed outer‐membrane protein patterns different from those of N. meningitidis in several molecular mass ranges. Cluster analysis based on expression of principal outer‐membrane proteins allowed the differentiation of commensal species and N. meningitidis, although not that of the invasive and carrier groups within the latter.