Number of patients with hypersensivities on dental materials increases continously. One of the most important allergens is benzoyl peroxide (BPO). BPO is part of the promoting system of acrylic denture materials. Aim of this study was to describe the BPO contents of denture materials after storage and different chemical treatments. 3 hot-curing acrylic resins, 2 self-curing acrylic resins and 1 microwave-curing denture material were investigated. BPO was measured in the polymer delivered by the manufacturer, after polymerization as recommended by the manufacturers, after extended polymerization (1 and 2h), after storage in water (aqua dest.) for 8 days, after storage in saliva (Fusayama,1963) for 8 days, after storage of 48h in KMnO4, alcohol and (NH4)2Fe(SO4)2. Indirect jodometry was used to detect BPO. BPO was found in all acrylic resins. However, there were significant differences between the resins (polymer 0,13 - 1,2 weight %, cured products 0,05 - 0,32 weight %) and differences between the specific treatments and storage procedures. The smallest effect on BPO showed (NH4)2Fe(SO4)2 after 48h (reduction 0 - 27 %). The strongest effect occured after extended polymerization for 2h (reduction 63 - 95 %). No reduction of BPO was seen after 8 days storage in water and artificial saliva. The microwave-curing material contented the lowest BPO-level of all materials. Under intraoral conditions it is unlikely that BPO is released from acrylic resin denture base materials. BPO in denture base materials can be reduced by extended polymerization. Schlagwörter: allergy, denture base materials, acrylic resin, BPO, MMA