The spore concentrations of Alternaria, a genera of microfungi widely considered as allergenic by different authors (Caplin & Haynes, Gravesen, Gregory, Larsen, Petersen & Sandberg), have been investigated in the atmosphere of Córdoba (Spain) during the period of April, 1983 to March, 1985 by means of the volumetric (Andersen sampler) and gravimetric (Durham based) methods, taking samples three times a day in culture media (Agar-Malt extract 2%) and incubating them for 5-7 days. The objectives of the work have been the establishment of seasonal variation patterns, as well as the possible correlations with the climatological factors. The results show that the different species of Alternaria detected are among the most important components in the aeromycoflora of the town, only exceeded by Cladosporium ssp., yeasts and Mycelia sterilia. In fact we found 3,283 colonies of Alternaria through the gravimetric method and 572 through the volumetric method, representing a 4.28% and 0.59% respectively of the total developed colonies during the sample period. The seasonal variations in air spore concentrations of Alternaria have also been studied monthly following the methods indicated above. It was found that January is always the month with less incidence of spores, with some days free of spores. May was the month with a maximum spores incidence during the first year of study, while this was delayed until june in the second year. This delay was probably due to the prolonged rainy season during the last spring. By establishing positive groups, A. alternata was found to be the most frequent species, with seven months during the period 1984-1985 exceeding the figure of 150 colonies per month.(ABSTRACT TRUNCATED AT 250 WORDS)