Fetal liver cells from individual embryos (littermates) were suspended, and equivalent numbers of fetal liver cells were plated in methyl cellulose for determination of BFU-E, CFU-GM, and CFU-Meg. Colonies were scored from triplicate plates and are expressed ±SD. There is a modest reduction in BFU-E in PDGFRβ^−/− fetal livers compared with PDGFRβ^+/+ (*P= .04).