A surgical mask, a coarse-dust mask and five types of fine-dust masks were tested by enhanced light microscopy and cross-sectional thickness measurements for their effectiveness against inhalation of cytostatic aerosols. The construction of surgical masks most nearly resembles that of coarse-dust masks with respect to quality and number of layers. They are thus not suitable as protection against inhalation of cytostatic aerosols. Such masks must be at least particle-filtering half-masks of type DIN 58645 FHM - P2 (fine-dust masks of protective stage P2).