Abstract A more sensitive quantitative immunoassay system was required for the forensic determination of ricin in animal tissue samples. A competitive enzyme-linked immunosorbent assay (ELISA) system has been previously described, with a maximum detection sensitivity of the order of Ing per 50 μl of tissue extract. This study reports the development of a highly sensitive ELISA, amplified using the avidin/biotin immunoperoxidase complex (ABC). With this system, the lower limit of detection for ricin has been improved considerably to the order of 20 pg per 100 μl of tissue extract. The method relies upon obtaining a solution of toxin by extracting tissue samples; the efficiency of this process is therefore critical for the success of the method. Extraction conditions have been examined and improved to maximise the opportunity for quantification of toxin.