During the last years the appearance of radiopaque concrements in the maxillary sinus was reported. These could be identified as root-filling material for teeth of the upper jaw containing zinc oxide. This suggested that excess root-filling material containing zinc oxide in the maxillary sinus could favour the development of a local, non-invasive aspergillosis. Therefore, we tested Aspergillus fumigatus, A. flavus, A. terreus, A. nidulans and A. niveus for the influence of zinc oxide. Cza-pek-Dox agar was inoculated with the six different Aspergillus strains. Circular cavities stamped into the agar's center of each plate were filled with aliquots of the dilutions of a geometric series of zinc oxide dissolved in 0,1n H2SO4. All plates were then incubated for seven days at 37 degrees C. Readings were taken on the 3rd, the 5th and the 7th day. It became obvious that solved zinc oxide promotes the growth of all the tested Aspergillus species. This influence diminished with decreasing concentration. This effect could be observed on all days of measurement. Only A. niger showed an attenuated dependence, probably due to the a priori high growth rate of this species on Czapek-Dox agar. It is concluded that overfilling of maxillary teeth with a zinc oxide containing root filling material favours the development of local aspergillosis.