The pathophysiology of endometriotic lesion development remains unclear but involves a complex interaction between ectopic endometrium and host peritoneal tissues. We hypothesised that disruption of this interaction was likely to suppress endometriotic lesion formation. We hoped to delineate the molecular and cellular dialogue between ectopic human endometrium and peritoneal tissues in nude mice, as a first step towards testing this hypothesis. Human endometrium was xenografted into nude mice and the resulting lesions were analysed using microarrays. A novel technique was developed that unambiguously determined whether RNA transcripts identified by the microarray analyses originated from human cells (endometrium) or mouse cells (stroma). Four key pathways (ubiquitin/proteosome, inflammation, tissue remodelling/repair and ras-mediated oncogenesis) were revealed, that demonstrated communication between host stromal cells and ectopic endometrium.