Thirty-three enterococcal strains and 10 Streptococcus bovis strains were investigated for their protein-binding cell surface components. Seven extracellular matrix (ECM) proteins were immobilized on Difco latex beads to detect these components on the surface of all enterococcal strains and eight non-autoaggregating S, bovis strains by a particle agglutination assay (PAA). Twenty-three selected strains were also examined in microtiter plate assays. According to the absorbance readings (A(570nm)), 11 strains were classified as nonadherent (A(570nm) < 0.1), 10 strains as weakly adherent (0.1 < A(570nm) > 0.3), and 2 strains as strongly adherent (A(570nm) > 0.3) in these assays. A direct correlation was found between the values obtained in PAA and A570nm readings of microtiter plate assays. Binding of I-125-labeled bovine lactoferrin to enterococci and streptococci was in the range of 6%-30% and of I-125-Iabeled human vitronectin in the range of 9%-33% to streptococci. The binding of I-125-labeled ECM proteins to selected strains was much more effectively inhibited by sulfated carbohydrates than by non-sulfated hyaluronic acid, indicating the importance of the sulfate groups of these inhibitors. An inhibition effect of heparin on bLf binding to four selected strains was higher in comparison with fucoidan in the microtiter plates. Thirty-five out of 44 strains had agglutinated rabbit erythrocytes. However, these strains showed no ability to agglutinate bovine or sheep erythrocytes.