Overexpression of soluble SCF increases the frequency of myeloid progenitors in the bone marrow. HPP-CFC and LPP-CFC assays were performed on bone marrow cells derived from various transgenic and nontransgenic white mice. Shown are total myeloid progenitors (ie, sum of all HPP and LPPs) from Sl/Sl^d (n = 22),Sl/Sl^d-S (n = 13),Sl/Sl^d-MR (n=  14), and wt (n = 20). HPP and LPP content were determined by multiplying the concentration of HPP-CFC or LPP-CFC by the total bone marrow cellularity. (*) P= .005, Sl/Sl^d-S versusSl/Sl^dand Sl/Sl^d-MR. The results show mean (×10³) ± SEM (bars).