The objectives of the study were (1) to assess total and specific antibodies in sera and saliva of secretors and non-secretors with reference to carriage of meningococci and smoking: (2) to assess the ability of saliva from secretors and non-secretors to inhibit bacterial binding to epithelial cells; (3) to assess bactericidal activity of sera from secretors and non-secretors. As a preliminary step, a sensitive precise and accurate enzyme linked immunosorbent assay (ELISA) was developed to assess the total and specific levels of IgA, IgM and IgG in serum and saliva. In a parallel trial, antibody levels obtained with the ELISA and SRID assay revealed that the ELISA was significantly more sensitive. Total serum and salivary IgG, IgA and IgM and levels of these isotypes specific for Neisseria lactamica and five isolates of meningococci were determined by ELISA from material obtained from 357 pupils and staff of a secondary school in which an outbreak of meningitis occurred. There were no differences in total or specific levels of serum IgG, IgA or IgM or salivary IgG or IgA of secretors compared with non-secretors. Non-secretors had significantly lower levels of total salivary IgM and lower levels of IgM specific for N.lactamica and five meningococcal isolates. No correlation between levels of serum and salivary IgM suggested that this IgM was produced locally and had not leaked from the serum. Although carriers had higher levels of antibodies than non-carriers, the effect of secretor status on antibody levels was still significant. Smoking had no effect on levels of total antibodies as those for neisseria. A flow cytometry assay was developed to assess the effect of salivary antibodies on the attachment of meningococci to epithelial cells.