The aim of the study was to determine the onset, duration and terminationof the ragweed pollen season; intradiurnal, daily and monthly pollen variation, and possible differencesin the occurrence and concentration of ragweed pollen according to sampling sites between 2002 and 2003.The study was conducted at three sampling sites in central Croatia over two pollen seasons (2002 and2003) using the volumetric method of sampling (Hirst type sampler). In 2003, the ragweed pollen seasonwas by 43 % longer and the percentage proportion of ragweed pollen by 3.4 % greater in comparison with2002. The total ragweed pollen count and number of days with ragweed pollen concentration greater than30 pollen grains per m (3) air showed a declining tendency from East to West in both seasons. The intradiurnalpeak concentration occurred between 10.00-14.00. The air concentration of ragweed pollen decreased withtemperature decline and precipitation. Results of the study provided useful information to individualsallergic to ragweed pollen thereby allowing them to adjust their outdoor activities to avoid contactwith the allergen.