Alternaria spores are found in the atmosphere in many locations around the world. They are significant from a human health perspective because they have been known to trigger allergic respiratory disease such as asthma and hay-fever. The presence of Alternaria spores in the atmosphere has been related to meteorological factors in past studies, but this has not been done previously in Sydney, Australia. This paper reports the results of such a study in Sydney. Alternaria spore concentration data for the period 19 August 1992 to 31 December 1995 were examined with meteorological data for the same period. The daily Alternaria spore concentration was compared to the meteorological data for the same day and for up to 3 days previously. The analysis methods were Spearman's rank correlation and multiple regression. Alternaria spores appear in the atmosphere of Sydney year-round, although they peak over spring, summer, and autumn. A number of meteorological factors, including mean, minimum, and maximum, temperature, dew point temperature, and air pressure, are significantly correlated with the atmospheric concentration of Alternaria spores. Some of these meteorological variables (temperature and dew point temperature) show significant correlations with a 1, 2, and 3 day lag, as well as for the same day. Regression models indicate that up to 31.1% of the variation in Alternaria spore concentration can be explained by meteorological factors. There is potential for the results of this study to be used by public health authorities in the prediction of Alternaria spore concentrations in Sydney.