Embryonal carcinoma (C) cells, the pluripotent stem cells of teratocarcinomas, show many similarities to embryonic stem (S) cells. Since EC cells are malignant but their terminally differentiated derivatives are not, understanding the molecular mechanisms that regulate their differentiation may be of value for diagnostic and therapeutic purposes. We have examined the expression of multiple components of two developmentally important cell-cell signalling pathways, Wnt and Notch, in the pluripotent human EC cell line, NTERA2, and the human ES cell line, H7. Both pathways have well-documented roles in controlling neurogenesis, a process that occurs largely in response to retinoic acid (A) treatment of NTERA2 cultures and spontaneously in H7 cultures. In NTERA2, many of the genes tested showed altered transcriptional regulation following treatment with RA. These include members of the frizzled gene family (FZD1, FZD3, FZD4, FZD5, FZD6), encoding receptors for Wnt proteins, the FrizzledRelated Protein family (SFRP1, SFRP2, FRZB, SFRP4), encoding soluble Wnt antagonists and also ligands and receptors of the Notch pathway (Dlk1, Jagged1; Notch1, Notch2, Notch3). Few differences were found in the repertoire of Wnt and Notch pathway genes expressed by NTERA2 EC cells and H7 ES cells. We present a model in which interactions between and regulation of Wnt and Notch signalling are important in maintaining EC/ES stem cells and also controlling their differentiation.