The dried aerial parts of Bidens pilosa L. were extracted with petrol ether, chloroform, methanol, and methanol/water. The petrol ether and the methanol/water extracts showed some antimicrobial activity. Fractionation of the extracts yielded well known substances, most of which have, however, not yet been described as constituents of Bidens pilosa. Several of these substances have previously been shown to be biologically active. Thus, phenylheptatriyne, linolic acid and linolenic acid have antimicrobial activities. On the other hand, friedelin and friedelan-3 beta-ol, as well as several of the flavonoids found are anti-inflammatory agents. The detection of these compounds in extracts from B. pilosa may rationalize the use of this plant in traditional medicine in the treatment of wounds, against inflammations and against bacterial infections of the gastrointestinal tract.