['The processes of tumour cell migration and invasion are enhanced by urokinase activity mediated by the urokinase receptor on the cell surface. Various factors affect the expression of the urokinase receptor, and amongst them we have found evidence that cell culture dispersity strongly upregulates it in breast cancer cell line BT 20.', 'Flow cytometry was used to quantify urokinase enzyme and urokinase receptors on the surfaces of cells cultured at different levels of dispersity.', 'Increasing the cell culture sparsity caused more than a doubling in the level of expression of the cell surface urokinase receptor in this cell line. A marked increase in the level of cell surface receptor-bound urokinase corresponding to the increase in the receptor itself also occurred in sparse cell cultures.'] Is urokinase receptor expression upregulated by cell culture sparsity in breast cancer cell line BT-20?