Roughly 10-15% of the population in Sweden suffers from allergic reactions from airborne pollen. One of the most common allergene pollen is the one from birch (Betula verrucosa and Betula pubescens). The pollen season is limited to a period of 3-4 weeks in spring. However, the start of the season varies at most ±2 weeks from year to year . The variation of pollen dispersion during the season also varies substantially between different years. Hypothesizing that these variations are related to exogenous processes, especially climatic influence, a simplified prediction model that simulates the aerobiological process has been developed. The model has been proven to give satisfactory results and was operationally tested for the Stockholm area during springtime 1981 and 1982.