An assessment of bat presence was conducted along the Norris-Madison Junction Road corridor in Yellowstone National Park, Wyoming during 20-25 September 1999. Twenty-three sites were monitored for bat activity; 21 sites were monitored overnight with electronic bat detectors, and two sties were mist-netted for 2.0-2.5 hr after sunset. Five bridges (including one just outside of the primary road corridor study area) were inspected for evidence of used by bats (droppings or roosting individuals), and one additional elevated wooden road structure spanning the outflow at a thermal feature was inspected for similar bat spoor. One undeveloped thermal area was checked for bat spoor around boulders because the area is a known maternity site by an unidentified bat species. Bats were recorded at 17 of 21 sites monitored with bat detectors; equipment malfunction occurred at one site. Species tentatively identified included Western Long-eared Myotis (Myotis evotis) at 3 sites, Big Brown Bat (Eptesicus fuscus) at 3 sites, and Silver-haired Bat (Lasionycteris noctivagans) at 5 sites. Unknown bat species were recorded at 11 sites, unidentified Myotis at 10 sits, and indistinguishable Big Brown/Silver-haired bat at 11 sites. The amount of bat activity (number of recorded passes) was relatively low at the majority of sites where bats were detected, ranging from 1-40 passes. Twelve or fewer passes were recorded at 12 of 17 sites, 20 or more passes were recorded at the remaining 5 sites where bats were detected. Two species of unidentified bats (one Myotis and one larger species) were observed foraging at crown level among lodgepole pines at the Norris Campground (B Loop and entrance area) between 19:40-21:15MDt. A few bats were observed at the two mist-netting sites, but only one bat was captured, a male Little Brown Myotis (M. lucifugus) along the Gibbon River below the Tuff cliffs picnic area. Bats observed at the second netting site (a small pond) were either Big Brown or Silver-haired bats. Three of six bridges or bridge-like structures had evidence of bat use. Three of four bridges with steel beams and concrete or stone pilings had concentrations of bat droppings on their undersides. The wooden structure at Beryl Springs and the concrete bridge spanning the Gibbon River at Madison Junction are probably used little if at all as a roost site by bats.