The aim of the study was to analyse the relationship between meteorological conditions and Alternaria and Cladosporium spore concentrations in the air of Zagreb in August 2002 and August 2003. These months were chosen because they represented climatic extremes. A 7-day VPPS 2000 Hirst volumetric pollen and spore trap was used for spore sampling. Spores marked as 'others' (ascospores, basidiospores, Epicoccum, Ustilago, Pithomyces, Helminthosporium, Stemphylium, Torula, Botrytis, Didymella) were found to have predominated in the month of August in both 2002 and 2003 with 91.1% and 70.5%, respectively. Because of favourable weather conditions (higher air temperature and minimal precipitation) in August 2003, the concentrations of Alternaria and Cladosporium spores were 3.4-fold those recorded in the same month in 2002. Also, the peak daily concentrations of these spores were measured on days without precipitation and with higher air temperature. Intradiuranal variation in the Alternaria and Cladosporium spore concentrations was identical in 2002 and 2003 (lowest in 2-hour interval between 06:00-08:00, and highest between 10:00-12:00). In spite of the three-fold increase in the Cladosporium spore concentration in August 2003, the borderline concentration of 3,000 spores/m3 air that is associated with the occurrence of allergic reactions was only exceeded on a single day. Air concentration of Alternaria spores exceeded borderline value of 100 spores/m3 air on as many as 17 days, suggesting that at that time of the year the risk of allergic reaction was only present in individuals allergic to this spore type.