Leafyeast populations were surveyed in 1987 and 1988 with the help of schoolchildren at 23 centres throughout Europe located at Brussels, Rochfort-Marche, Flobecq-Renaix and Tournai (Belgium); Aberdeen and Halifax (Britain); Lyon, Rouen and Toulouse (France); Hamburg, Koblenz and Stuttgart (Federal Republic of Germany); Banbridge, Belfast, Dublin and Enniskillen (Ireland); Hollenfels and Ettenbruck (Luxembourg); Apeldoorn, Deventer, Harlem, Leiderdorp and Zutphen (Netherlands). From one to one hundred schools were involved at each centre. The results demonstrate the suitability of leafyeasts for assessing air quality in both urban and rural areas of the non-Mediterranean countries of Europe. Low counts are associated with known pollution sources. As leafyeast populations change quite quickly, the effect of weather systems on the impact of pollution clouds from urban/industrial areas can be followed. Leafyeasts thus give information complementary to that from traditional biological monitors like lichens which provide an integrated picture of the pattern of air pollution over the months or years prior to study.