A double sandwich ELISA system has been produced capable of detecting < 166 ppm bovine and ovine heat‐stable proteins in rendered animal material heated to 140°C for 1.5 h. Removal of gelatin from rendered animal material by ammonium sulphate precipitation and concentration of the remaining proteins for species testing proved to be of considerable benefit in amplification of test sensitivity.* Increased sensitivity was also obtained by judicious selection of antisera raised either against fresh’ or ‘cooked’ muscle/ tissue heat‐stable antigens.