An estimate of the extent of depletion of colony-stimulating factors in culture.

Between 30 and 40% of the CSF present in agar was depleted after culture for 1 week with 50,000 nucleated murine bone marrow cells. No statistically significant difference could be detected between this depletion and the extent of depletion of CSF when the amount present was halved. There was no evidence that toxic or inhibitory products reduced the colony count in the group to which stored CSF had been added.