The understanding of the mechanisms of biological activities and biotransformation of trace elements such as arsenic and mercury has improved during recent years with the help of chemical speciation studies. However, the most important practical application of elemental speciation is in the area of toxicology. Toxicological knowledge on the individual chemical elemental species of heavy metals can lead to more specific legislation of hazardous substances found in feed . Examples here are arsenic, where the inorganic forms are the most toxic, whereas for mercury the organic form methylmercury is more toxic than inorganic mercury. In this presentation an overview of the current knowledge on arsenic and mercury speciation in feed and analytical methodologies for arsenic and mercury speciation analysis will be given. Additionally the current status in legislation for heavy metals in feed and also initiatives for the establishment of standardised methods for determination of inorganic arsenic and methylmercury will be presented. The lecture focuses on the present situation for speciation in feed control and discuss the latest and expected future developments within this area .