Several toxic substances have been detected in plants which are responsible for animal and human diseases.Bracken fern (Pteridium aquilinum) is one example, widely distributed in many parts of the world. It is knownto cause cancer in humans and other animals. In fact, man can be directly or indirectly exposed to the dangerby consuming fern, contaminated water, milk, meat, and spore inhalation. Experimental studies have shown anassociation between bracken exposure and gastric cancer, and research has shown genotoxic and cytotoxic effectsin vitro. This paper describes and reviews toxic, carcinogenic, genotoxic/cytotoxic, and immunomodulatory effectsof bracken and included possible toxic agents. The chemistry of Ptaquiloside (PT) reactions is emphasized, alongwith bracken problems in livestock, possible pathways of exposure in man, and control for human health.