Mucosal surfaces are prominent in the gastrointestinal, urogenital, and respiratory tracts and provide portals of entry for pathogens. The mucosal immune system consists of molecules, cells, and organised lymphoid structures intended to provide immunity to pathogens that impinge upon mucosal surfaces. The aim of this study was to assess humoral immunity in the vaginal mucosa and compare this immune response to a systemic response. The use of commercially available tampons provided a self-administered, pain free method for the collection of vaginal secretions. To standardise specimens, a total protein determination was performed on vaginal secretions and on sera. All subjects were screened for sexually transmitted infections (STIs) using conventional and deoxyribonucleic acid (DNA) amplification tests. Immunoglobulin levels in vaginal secretions and in sera were quantitated using a quantitative sandwich enzyme- linked- immunosorbent assay (ELISA). The immunoglobulin levels quantitated were analysed on the basis of pregnancy status and the presence or absence of an STI. Immunoglobulin results for serum showed a significant increase in IgG and IgA in women with an STI regardless of pregnancy (p< 0.001). This study showed a decrease in vaginal IgG and IgA in women with an STI. Non-pregnant women with an STI had significantly lower levels of IgG and IgA in the cervico-vaginal secretions as compared to the controls (p=0.002 and p=0.0002 respectively). This was also observed in pregnant women (p= 0.03 and p< 0.001 respectively). IgM levels were mostly too low to be detectable but showed a tendency to increase in vaginal secretions of women with an STI. Pregnancy did not have an effect on immunoglobulin levels except for IgA. The effects observed were due to the presence of an STI. All the STI pathogens studied displayed a similar effect on immunoglobulin levels. Bacterial vaginosis, however, appears to exert an effect specifically on lowering IgG (p=0.008) in vaginal fluid and increasing IgG levels (p=0.008) in serum. Once a more complete understanding of the mechanisms associated with the host defence of the vaginal mucosa is obtained, specific immunotherapeutic strategies can be developed. A greater knowledge of host defence factors specific to the vagina will provide insights into understanding susceptibility to opportunistic infections and STIs. / Thesis (M.Med.Sc.)-University of Natal, 2003.