BS II lectin, a second hemagglutinin isolated from Bandeiraea simplicifolia seeds, agglutinated the red cells from 11 patients manifesting the ‘acquired B’ antigen phenomenon. The results of serological studies indicate that this lectin has specificity for the type III polyagglutinable receptors rather than for the ‘B-like’ antigens present on ‘acquired B’ red cells. Two other blood samples which did not possess ‘acquired B’ antigens were also found to react with BS II lectin. Both of these samples were shown to have properties similar to those reported for Tk red cells. The serological characteristics of red cells modified in vitro by a culture broth of Bacteroides fragilis suggest that type III polyagglutinable receptors are identical to those associated with Tk red cells.