After detecting many carcinogenic compounds of plant origin in the last 10–20 years, a survey was given about their structure, occurrence and carcinogenic actions on animals. Pyrrolizidine alkaloids are found in the genera Senecio, Crotalaria and Heliotropium; cycasine in Cycas species; safrole in Sassafras species and sanguinarine in Papaver and Fumaria species etc.