We studied the relationship among (1) the characteristic weather types found in the Carpathian Basin in the summer to early autumn period (July 15 to October 15) and in the winter months (December, January and February), (2) the levels of chemical (CO, NO, NO 2 , NO 2 /NO, O 3 , O 3max , SO 2 , PM 10 ) and biological (pollen) air pollutants, and (3) their effect on respiratory diseases. The database comprises daily values of 13 meteorological parameters, 8 chemical and 8 biological pollutants, and the number of patients for the period from 1999 to 2003, in Szeged, Hungary. Altogether, 9 symptom groups of respiratory diseases and their occurrences were taken into account. In the summer to early autumn period a total of 26 703 patients, while in the winter months a total of 14 507 patients, registered with respiratory diseases were considered. An objective definition of the characteristic weather types was carried out by using factor and cluster analysis. In the winter months, there was no relationship between the 8 defined weather types and patient numbers. On the other hand, in the summer to early autumn period, Weather Type 7, with a weak anticyclonic ridge character and the highest patient numbers, was linked to high temperature parameters (T mean , T max , T min ), low relative humidity, as well as high chemical and biological pollutant levels. At the same time, Type 2 (anticyclonic ridge character) was associated with the lowest patient numbers and was characterized by high temperature and medium relative humidity parameters, as well as high levels of chemical and low levels of biological air pollutants. Results on the relationships of the meteorological parameters and chemical air pollutants, as well as weather types, will be built into a model to predict, and in this way to prepare for, days of severe risk of respiratory illness.
