A program to close abandoned mines on BLM lands in southwestern Montana is scheduled. Some of these mines may provide habitat for up to 15 species of bats, including six U.S. fish and Wildlife Service Designated Species of Concern (former category 2 species). The USGS biological Resources Division provided funding to the Montana Natural Heritage Program to survey abandoned mines in southwest Montana for bat use. The objective of this study is to identify mines used by bats and evaluate a variety of external and internal variables that would enhance predictive capabilities for locating active roosts and hibernacula. The results of this study will assist in avoiding the elimination of habitat that may be important to bats. Fieldwork was initiated on August 18, 1997 and continued through October 15, 1997. Eighty-six abandoned and inactive mines were visited. Sixty-eight mines had one or more openings that might be suitable for bats. Openings had completely collapsed or were backfilled at 18 mines. Eleven mines were rated as having high potential to provide bat habitat. Mines which appeared to have the best potential for current bat use included the Bluewing, Clipper, Hendricks, Huron/Cottontail, Keystone, Shoemaker, and an unnamed cluster of shafts near the Watseca mine. These mines were extensive with complex workings that may interconnect underground, facilitating air flow through the mine. Mines in the Bannack mining district appeared to be the most stable and exhibit the greatest potential for internal surveys. These mines were mostly located in limestone substrate. Most mines in the Rochester mining district were situated in oxidized shists that were very friable and appeared to be quite unstable and unsuitable for internal surveys. External monitoring for bat activity was conducted at 66 openings from 34 mines. Ultrasonic monitoring was conducted at 59 openings; while mist-netting was conducted at eight locations. Bat activity was documented at 24 mines. However, analysis of ultrasonic recording is currently in progress, which may reveal more activity. Tentative bat species detected by ultrasonic methods include unidentified Myotis species, western long-footed myotis (Myotis evotis), silver-haired bat (Lasionycteris noctivagans), big brown bat (Eptesicus fuscus), and possibly the Townsend big-eared bat (Corynorhinus townsendii). Myotis ciliolabrum and M. evotis were the only species captured in mist nets, with 17 and three captures, respectively. Most captures were of adult non-reproductive males, while only one adult non-reproductive female M. ciliolabrum and one juvenile male M. ciliolabrum were captured. Development of a GIS database of mine locations and sampled openings is in progress. Field-survey data are being entered into appropriate data tables and linked to a master database obtained from the Montana Bureau of Mines and Geology.