To take preventative measures to protect allergic people from the severityof the pollen season, one of aerobiology's objectives is to develop statistical models enabling the short-and long-term prediction of atmospheric pollen concentrations. During recent years some attempts havebeen made to apply Time Series analysis, frequently used in biomedical studies and atmospheric contaminationto pollen series. The aim of this study is to understand the behaviour of atmospheric alder pollen concentrationsin northwest Spain in order to develop predictive models of pollen concentrations by using Time Seriesanalysis. The prediction line proposed for Oviedo and Ponferrada are similar (Arima 2,0,1) while in Vigoa more accurate model founded by Arima (3,0,1) and in Leon (1,0,1) was used. The results suggest thatPonferrada and Oviedo are the cities in northwest Spain where Alnus pollen allergic individuals shouldto take preventive measures to protect themselves from the severity of the pollen season. Alnus pollenvalues higher than 30 grains/m3, a quantity considered sufficient to trigger severe allergy symptomsof other trees of the Betulaceae family, could be reached during 25 days in some years. The predictedlines conformed with the observed values overall in the case of Leon and Ponferrada. Time Series regressionmodels are especially suitable in allergology for evaluating short-term effects of time-varying pollenappearance in the atmosphere.