A technique for examining relatively large volumes of bone marrow for involvement by malignancy is described. The use of discontinuous Percoll gradients offers no advantage over conventional methods in the diagnosis of hematological malignancy. Its usefulness in detecting infiltration by solid tumor is uncertain. Complete exclusion of malignancy from the fraction containing hematologic stem cells in three patients raises the possibility that this technique is a useful adjunct to other methods of marrow purging before autologous marrow rescue in malignant disease.

A microassay for human committed progenitor cells (CFU-c) has been developed using 24-well, 16 mm diameter culture dishes. Comparisons were made of simultaneous cultures of 21 samples in both 35 mm and 16 mm culture dishes employing two sources of colony-stimulating factor (CSF). The microassay does not differ significantly from the standard 1 ml 35 mm assay, apart from some enhancement of colony numbers in the 16 mm dish. Other advantages of the microassay are that it is economical with respect to cells, media, and space; and it is possible to increase the number of experiments fivefold which can be performed with the same number of cells.