A number of human disorders are characterized by degeneration or loss of specific cells, resulting in pathology associated with reduction or absence of cell function. Such diseases include neurodegenerative diseases and diabetes. Methods are described for obtaining a substantially homogeneous population of undifferentiated human embryonic stem cells including incubating a population of human embryonic stem cells with an amount of a selection agent. The selection agent is effective to reduce or eliminate differentiated embryonic stem cells from the population of cells such that a substantially homogeneous population of undifferentiated human embryonic stem cells is obtained. The substantially homogeneous population of undifferentiated embryonic stem cells may be produced without use of feeder cells.