Pipistrellus pipistrellus, Eptesicus serotinus, Nyctalus noctula, N. leisleri, Myotis daubentonii, M. myotis, unidentified small Myotis spp. and Plecotus spp. were recorded during bat detector transects within a central European city of 350,000 inhabitants. Bats were recorded in all seven habitat types under study, the levels of activity for each species and habitat type were significantly different. The relative activity of the whole bat community was highest in old outskirts (low density housing) and at the river, and lowest in the city centre and new housing estates (high density housing). Significant differences were found in the timing of bat activity during the night and the season. Within the first two hours after sunset, relative activity of P. pipistrellus and E. serotinus was highest in the first 0.5 h and decreased thereafter. In N. noctula, it was highest during the second and third 0.5 h and in Myotis spp. it was low in the first 0.5 h and increased till the end of monitoring. Flying bats were recorded from March till October; the lunar cycle had no significant effect on the amount of flight activity. The relative activity of E. serotinus was positively correlated with temperature. No significant correlation was found between the activity of bats and the number of trees and streetlamps per transect. Comparison with the results of an earlier visual census showed that more bats were recorded acoustically than visually except in the city centre. This is attributed to the effect of white streetlamps during the visual census. During the acoustic census, most white lamps were replaced by yellow lamps which biased the impact of lamps on bat traffic. Nevertheless, bat species known to benefit from white streetlamps remained the most common foragers within the city.