Propolis is a resinous product of the honeybee Apis mellifera L. and the stingless meliponines with an antibacterial, antifungal, antiviral, antiphlogistic and immunostimulant effect. In folk- and alternative medicine Propolis is primarily used to cure skin diseases and skin injuries, as well as common colds. In the course of this diploma thesis three commercial propolis extracts from different Austrian sources were analysed regarding their antimycobacterial activity and their antibiotic resistance-modulating effect.The tests were carried out based on microdilution assays against M. smegmatis mc2 155 ATCC 700084, a nonpathogenic member of the family Mycobacteriaceae which includes, amongst others, the pathogens of tuberculosis and leprosy.Thereupon one of the three propolis extracts was ? by dint of different chromatographic methods ? separated in fractions and their chemical profiles were investigated by LC-ESI-MS analysis. The aim was to find out which compounds are accountable for the antimycobacterial and antibiotic resistance-modulating effects, respectively, again by using bioassays. Especially in combination with rifampicin the propolis extracts had a considerably resistance-modulating effect.A particularly good modulating-activity could be confirmed for the combination of quercetin with isoniazid (MF = 32) and the combination of caffeic acid with rifampicin (MF = 8). Furthermore, caffeic acid proved to be a good modulator in combination with isoniazid (MF = 4), and pinocembrin had a considerably modulating effect in combination with ethidium bromide (MF = 2-4), a substrate of many bacterial efflux pumps.