The distribution and abundance of cave-dwelling bats were investigated in the Thrace region of northwest Turkey. Data were collected in two periods, January-March and April-May 2001, from 32 underground sites, 25 of which had not been surveyed previously. Approximately 76,000 bats representing 13 species were recorded. The most abundant species were Miniopterus schreibersii, Rhinolophus euryale, Myotis myotis/blythii, Myotis capaccinii, and Rhinolophus ferrumequinum. The roosts were evaluated for their conservation importance. The most important sites in Turkish Thrace are Dupnisa and Koyunbaba. The Dupnisa Cave serves as a hibernaculum to approximately 28,000 bats representing five species. The Koyunbaba Cave is a nursery roost to approximately 23,000 bats of six species. Presently, none of the caves in the region has adequate protection and some bat populations are under serious threat. (C) 2004 Elsevier Ltd. All rights reserved.