Bone-marrow cells from patients with acute leukemia in remission were tested for their capacity to produce a substance (leukemia-associated inhibitory activity, LIA) that inhibits the formation of granulocyte and macrophage colonies in cultures of normal, but not of leukemic, bone marrow. LIA was detected in extracts of whole marrow in only eight of 83 patients in remission. However, extracts of slowly sedimenting cells, separated by velocity sedimentation from the marrows of eight patients in remission whose whole marrow had produced no LIA, produced inhibitory material in all cases. Extracts of the more rapidly sedimenting cells from these marrows contained an inactivator of LIA. Three of six patients in remission whose unfractionated marrow was unresponsive to LIA had a subpopulation of colony-forming cells that was sensitive to the inhibitor. These observations suggest that certain cellular functions dot not completely return to normal during remission of acute leukemia.
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