The presence and prevalence of common saprophytic airborne microfungi has been studied. Since August 1977 culturable microfungi in the outdoor air of Copenhagen have been monitored. The method used is a volumetric analysis by means of a Biap Slit-Sampler. The microfungal flora was dominated by very few genera, thus Cladosporium, Alternaria, Penicillium and Aspergillus make up 86.8% of the organisms collected. The mere number of microfungal spores might be misleading as a guide to the relative importance of atmospheric allergens. An alternative or a supplementary parameters could be the spore substance expressed as cubic spore substance/m3 of air, as suggested by Hyde (20). Most fungi show a seasonal dependence as well as fluctuations from year to year. The high season for living microfungi is found to be from June until October. The microfungi thus constitute a prolongation of the pollen season, a fact of importance in relation to patients suffering from inhalation-allergy.