The level of host proteins in 3-day supragingival plaque extracts was compared in caries-resistant (CR) and caries-susceptible (CS) adults with little or no gingival inflammation to minimize the contribution of gingival crevicular fluid ( GCF ). Except for IgA, all the host proteins examined were present at similar levels in both groups of subjects. Although the IgA exhibited fragmentation on sodium dodecylsulphate gradient-polyacrylamide gel electrophoresis (SDS-PAGE) and transfer electrophoresis in both groups, the amount of binding to a standard antisecretory IgA antiserum was higher in CR than in CS subjects. This could be a reflection of the trend towards a higher concentration of IgA in saliva of CR subjects or the result of less proteolytic activity in CR plaque. Even in 3-day plaque in the absence of gingival inflammation, GCF contributes a significant share of the host proteins to plaque extracts. Salivary proteins in plaque do not parallel their relative concentration in saliva.