"Delvocid" (Gist Brocades nv.) a preparation containing the natamycin, a substance used in the therapeutics, is used in cheese making to protect a cheese surface against mould development. This preparation is added either to polyvinyl acetate (PVA) used for cheese coating or as an aqueous suspension in which cheese is immersed before the ripening. The natamycin content in the outer layer of cheese was determinated by a spectrophotometric method. During maturation of cheese coated with natamycin-containing polyvinyl acetate, the natamycin did not migrate into the cheese. The natamycine concentration in cheeses that had been immersed in an aqueous solution of natamycin was considerably higher than that in PVA-coated cheeses and was related to the type of cheese, concentration of the "Delvocid" preparation, the length of time for which the cheese was held in solution.