The horse-chestnut leafminer is a new pest which was established in North-West Hungary ca. 10 years prior to these investigations. Due to the very limited time, there are relatively few studies on the parasitoid community of the moth and its connection with the leafminer host. Authors used twig-isolators to find out which larval/pupal instars are mostly parasitized and by which chalcidoid species. They also made an attempt to calculate density curves of different developmental stages of the moth and to compare them with flight curves of the parasitoids. Experiences indicated that 4-week-old larval (pupal) instars were parasitized to the highest degree. The most frequent parasitoids were Pediobius saulius and Pnigalio agraules . Statements about a poor synchronization between moth and parasitoids were confirmed but possibility of a shift in swarming times on location was suggested. Different methods to calculate rate of parasitism were compared and evaluated. © 2009 Akadémiai Kiadó.