Species composition of galls on the leaves of Ulmus laevis Pall. was analysed in 2001 – 02 in the Mogilski Forest – near an urban agglomeration of Kraków. A total of 5830 galls were found. The galls were caused by 5 insect or mite species. Aceria ulmicola brevipunctata (Nalepa) was the most abundant species in both years.
The index of occurrence frequency and Agrell's index of species co-occurrence have been calculated. The index of occurrence frequency (F) reached the highest value in the case of A. ulmicola brevipunctata, namely 1.740, in 2001, and the lowest value, i. e. 0.00 005 for Schizoneura ulmi (Linné), in 2001. Agrell's index of species co-occurrence reached the highest values, i. e. 0.500, in the case of A. ulmicola brevipunctata and Physemocecis ulmi (Kieffer), in 2002, and the lowest one, namely 0.050 for A. ulmicola brevipunctata and Schizoneura ulmi, in 2001.