Bone marrow long-term cultures were studied for 8 weeks in four experiments before and after T-cell depletion with a mixture of monoclonal antibodies directed against CD2, CD5 and CD7. No differences in cellularity or granulomonocytic progenitor numbers appeared during the period of culture. We conclude that in vitro treatment in itself is not likely to explain non-take or graft rejection associated with T-depleted bone marrow transplantation.