Abstract: A process for preparing a stable receptor preparation suitable for the quantitative determination of substances able to bind to cerebral receptors in which a brain or brain-region material is homogenized with an aqueous solution of an inert substance soluble in water; the formed homogenizate is centrifuged at an acceleration of 800 to 110 g for 8 to 20 minutes to form a supernatant; the brain or brain-region material is isolated from the supernatant by centrifuging the supernatant at an acceleration of 18,000 to 22,000 g for 10 to 20 minutes, the thus-obtained solid substance is rehomogenized in distilled water; the homogenizate is frozen and then thawed and thereafter centrifuged at an acceleration of 7000 to 9000 g for 5-15 minutes; the supernatant is isolated, centrifuged at an acceleration of 35,000 to 45,000 g for 20 to 30 minutes; the obtained solid substance is washed with an aqueous buffer solution of a pH value between 6 and 8, and a suspension consisting of the solid substance and the washing liquid