It was reported that monoclonal antibody (MoAb) J11d.2 reacts with mature blood cells of mice but not with their progenitors. We tested in culture studies whether this antibody could be used for enrichment for primitive marrow progenitors. The majority of colony-forming cells including multipotential progenitors in the marrow cells from 5- fluorouracil (5-FU)-treated mice were J11d.2+, whereas most of the progenitors from normal mice were J11d.2-. In addition, formation of multilineage colonies from J11d.2+ in both 5-FU-treated and normal mice was augmented by interleukin 6. These observations indicated that MoAb J11d.2 recognizes cell cycle-dormant progenitors. We have recently described a simple method that provides 800-fold enrichment for the progenitors in post-5-FU marrow cells using MoAb D7 (anti-Ly-6A/E). When this method was modified to include sorting with MoAb J11d.2, D7+ J11d.2+ cells were 2,250-fold enriched for multipotential progenitors. Micromanipulation and culture of individual D7+ J11d.2+ cells showed that average plating efficiency of the cell population is approximately 70% and that about 30% of the progenitors are lymphohematopoietic in nature. These data demonstrate that J11d.2 is a useful MoAb for the isolation of primitive hematopoietic progenitors of mice.