Using a differential centrifugation method followed by culture in selective medium, we have successfully isolated and maintained individual epithelial and stromal cells from normal (n = 10) and malignant (n = 6) human breast tissue and characterised their phenotype by immunocytochemistry. Further, we have studied expression of the cytokine genes IL-I p, IL-6, IL-8 and TNF-P in each cell fraction by RT-PCR and have compared these results with cytokine gene expression in tissue extracts from which primary cultures were derived. In breast tumours, there was near complete absence of IL-I p in both whole tissue and cell fractions, and in normals it was present in only 3/ I0 tissue preparations, with increased expression in stromal(6/ 10) and epithelial (5/ 10) cell samples. IL-6 was constitutively expressed in all tumour-derived breast tissue samples but downregulated in tumour cell cultures, with the opposite result in normal breast. Near identical levels of IL-8 expression were found throughout each preparation, irrespective of tissue origin. TNF-P was expressed in all normal tissue samples, in 9 / I0 epithelial preparations but in only 6/ 10 stromal preparations. In tumours, TNF-f3 was associated predominantly with whole tissue or stromal samples, with reduced expression in epithelial preparations. Our data confirm that primary cultures of normal and malignant human breast tissue can be successfully separated into epithelial and mesenchyrnal cell populations and their phenotype can be maintained in culture for up to 30 days. However, this cellular separation does alter the cytokine profiles; therefore, experimental findings with isolated cells should be treated with a caveat.