Factors controlling the differentiation of the multipotent embryonic lung endoderm and mesoderm are poorly understood. Recent evidence that Delta-like 1 (Dll1) and other genes in the Notch/Delta signaling pathway are expressed in the embryonic mouse lung suggests that this pathway is important for cell fate decisions and/or the differentiation of lung cell types. Here, we report the localization of transcripts of several genes encoding members of the Notch/Delta pathway in the early mouse lung. Most genes are expressed in specific populations and so may contribute to cell diversification.