Mouse bone marrow and spleen cells agglutinated by soybean agglutinin (SBA) or peanut agglutinin (PNA) were previously shown to be enriched for spleen colony-forming cells (CFU-S) and sufficiently depleted of graft-versus-host reaction producing cells to allow hematologic reconstitution of lethally irradiated allogeneic recipient mice. A similar enrichment for cells capable of forming colonies in soft agar culture (CFU-C) has now been found in the SBA-agglutinated fraction of mouse bone marrow cells, in contrast to the finding that in human bone marrow the majority of the CFU-C are in the fraction not agglutinated by SBA. Cytofluorometric studies with fluorescein-labeled SBA (FITC- SBA) revealed that the majority of both mouse and human bone marrow cells bind the lectin. Experiments mixing the human marrow fractions separated by SBA reveal that true enrichment for CFU-C is achieved in the unagglutinated fraction, as opposed to a possible depletion of a suppressor cell population. Granulocytic, monocytic, and mixed cell colonies were all enriched in the SBA-unagglutinated cell fraction from human bone marrow.