Cells transformed by Friend virus in liquid suspension culture respond to low concentrations of dimethylsulfoxide by initiating hemoglobin synthesis. The kinetics of appearance of such differentiated erythroid cells is consistent with either the induction of differentiation in a uniformly susceptible population of transformed cells or selection for the growth of a distinct erythropoietic subpopulation. The dimethylsulfoxide response of individual colonies of cells transformed by Friend virus grown in semisolid medium was studied in order to distinguish between these alternatives. The data do not support a selective effect of dimethylsulfoxide on the growth of a unique erythropoietic subpopulation; they indicate, rather, that the 745A strain of cells transformed by Friend virus consists of a relatively uniform population of dimethylsulfoxide-sensitive erythropoietic cells.