Abstract: There is provided a method for producing purified P-glycoprotein (P-gp) in a stabilised form such that, after being reconstituted into proteoliposomes, it can be freeze dried and stored for prolonged periods of time without loss of biological activity The method comprises the steps of: i) solubilising a mixture of P-gp and other proteins obtained from cell membranes; ii) removing insoluble material by centrifugation; iii) placing the mixture of P-gp and other proteins in a purification column; and iv) running through the purification column at least one wash buffer so as to remove unwanted proteins, and then at least one elution buffer so as to recover the P-gp; wherein one or more of the buffers contains a disaccharide. Trehalose is a particularly preferred disaccharide.