Effect of rhCDD on mouse bone marrow GM-CFC in the presence (•) or absence (○) of 10^-4 mol/L thymidine. The cells were cultured for 7 days in a GM-CFC agar assay with 10% CM 5637 as stimulator. Colonies of more than 50 cells were counted. Mean values ± standard deviation (SD) are given as percent of controls.