PM(10) and PM(2.5) fractions were collected by high-volume cascade impactors during 4-week periods in spring, summer and winter seasons in Amsterdam, Lodz, Oslo and Rome and at a Dutch seaside site. The samples were screened for respiratory allergy potential with the mouse popliteal lymph node (PLN) and the ELISA-based IgE antibody assays. For inflammatory screening, release of the cytokine macrophage inflammatory protein-2 (MIP-2) from primary rat type 2 cells was determined. Most fractions gave an increase in the lymph node response with the model allergen ovalbumin indicating adjuvant activity. Some of the coarse fractions gave a lymph node response even in the absence of ovalbumin, caused probably by non-specific inflammation. With the exception of a few of the coarse fractions, all ambient fractions increased the production of specific IgE. Fine particles had stronger adjuvant effect than coarse particles. A significant increase in the allergen specific IgG2a response was observed for the fine and some of the coarse fractions, indicating a non-allergic Th1 response. No consistent differences in adjuvant effects between the locations were observed. Particle samples collected in the different European cities differed in their potency to induce MIP-2 in type 2 cells. Coarse fractions of the urban particles samples, as well as the coarse fraction collected at the seaside, were more potent than the fine fractions to induce MIP-2. With respect to seasonal variations, the coarse fractions collected in summer seemed to be the most potent.