With the loss or modification of natural roosting habitat afforded by caves, abandoned mines have assumed increased importance as surrogate roosting sites for Townsend's big-eared bats (Corynorhinus townsendii) and other chiropteran species. However, increasing concerns for human safety have led to accelerated programs for mine closure. In efforts to protect roosting sites in mines showing significant bat activity, "bat compatible" gates are installed, thus allowing continued access to mine workings. Aside from ensuring public safety, these structures afford protection from disturbance to roosting bats. To date few posting-gating studies have been conducted to obtain information on the effects of these structures on bat behavior and roost suitability. I evaluated the effects of gating on bat flight patterns at maternity colonies in two previously gated (reference) and two ungated mines, the latter (treatment) being gated with roundbar Manganal steel gates in the second year of the study. I also monitored four gated and three treatment mines to determine the potential effects of reclamation on internal microclimate. Overall circling activity increased > 6-fold at the portals of treatment mines following gating. Indices of crowding and frequency of bat-gate collisions were significantly higher in previously gated and increased substantially in treatment mines following reclamation. Gates appeared especially hazardous to subadults during initial-volancy periods. Increased activity of bats and collisions with gates at mine portals may amplify vulnerability to potential predators. Changes in internal mine microclimates, specifically increased ranges between minima and maxima in temperature and vapor pressure deficits following reclamation varied among treatment mines as a function of the number of mine openings. Generally, gated mines with multiple openings experienced greater changes in these parameters than those with single openings. Additional studies of bat-compatible gates are needed to elucidate possible long-term effects of these structures on Townsend's big-eared bats.