The latest developments in DNA research have had an immediate impact on numerous life science disciplines. Among many applications of molecular genetics to forensic toxicology, the determination of species and geographic origin of illegal plants seems to be one of the most promising. This paper presents a variety of methods available for forensic DNA typing of narcotic plants (mainly Cannabis sativa L.). We also present recent findings concerning the action of xenobotics on a molecular and genetic level, and discuss prospects for their use in forensic toxicology practice.