The prostate is composed mainly of epithelial and stromal cells, whose dynamic interaction is vital to a broad array of cellular processes, including proliferation, differentiation, growth, and apoptosis. To understand intercellular communication in the development and progression of prostatic diseases, we examined gene expression in tissues from five patients diagnosed with benign prostatic hyperplasia (BPH). Fibroblasts and epithelial cells derived from these tissues were grown in a primary co-culture system that retains many characteristics of the intact human prostate. The mRNA levels of expressed genes as assessed by differential-display reverse transcription-PCR revealed that 110 genes were differentially expressed in co-cultured fibroblasts and epithelial cells, compared with expression in separately cultured cells. Eighty-four of these were confirmed by reverse Northern blotting, and 68 were successfully sequenced. Of the sequenced genes, 43 were differentially expressed in epithelial cells (37 upregulated, 6 downregulated), and 25 were differentially expressed in fibroblasts (6 upregulated, 19 downregulated) in co-cultures versus separate cultures. Semi-quantitative RT-PCR analysis of 12 genes with known functions showed that five of these were differentially expressed in co-cultured cells. Human kallikrein gene 7 (KLK7) was markedly upregulated in co-cultured compared with separately cultured epithelial cells (P<0.001), whereas S100 calcium binding protein All, tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, cyclin I, and latexin were significantly downregulated in co-cultured fibroblasts (P<0.05). Quantitative real-time RT-PCR and Western blot analysis confirmed KLK7 up-regulation at both the mRNA and protein levels, respectively. Thus, epithelial-stromal cell interaction and communication are likely to be important in BPH. Epithelial cells and fibroblasts may interplay coordinately or collaboratively to influence cellular growth and death through dynamically differential gene expression in response to physiological and pathophysiological changes.