Methods are described for mapping a pathway of differentiation of a population of embryonic cells which includes exposing the cells to an exogenous factor and measuring gene expression products that are characteristic of a particular cell type or lineage. Directing differentiation of human embryonic cells relies on dissociated embryoid bodies which are then exposed to one or more exogenous factors to enrich a culture for a particular cell type. The differentiated cells may be used for treating a medical condition in a human. Kits for determining differentiation pathways and screening exogenous factors for their utility in differentiation are provided.