The results presented indicate that blocking curves of decreased slope are obtained with the Talmage test when the labelled antibody eluate contains a portion of antibody which is not represented in the unknown serum. The blocking curves of late antisera had steeper slopes than those of early antisera when tested against labelled antibody eluates prepared from late antisera. This situation was reversed when labelled eluates from early antisera were used in the Talmage test. The findings were interpreted to indicate that early antisera did not have a full complement of antibodies, directed against all surface antigens of the bacterial cell.