Antisera prepared in rabbits by immunization with p-aminophenyl I-kojibioside conjugated to bovine serum albumin (antikojibiose sera), readily agglutinated whole cells of Streptococcusfaecalis or Streptococcusfaecium, and showed specific reactions with the lipoteichoic acids (LTAs) of these streptococci by passive hemagglutination, microscale enzyme-linked immunosorbent assay, and crossed immunoelectrophoresis. The interaction of the antikojibiose sera with the LTAs was inhibited best by kojibiose [a-D-glucopyranosyl-(1-2)-D-glucose], somewhat less by the dextran from which the kojibiose was prepared, and not measurably by maltose [a-Dglucopyranosyl-(1-+4)-D-glucose]. The sera reacted only minimally in only the most sensitive assay (microscale enzyme-linked immunosorbent assay) with LTA from group A streptococci (this LTA contains a single kojibiosyl residue as part of the glycolipid moiety of the molecule and failed to react with the Lactobacillus fermentum LTA which is substituted with aD -galactopyranosyl-(1-2)-D-glucosyl units.