An immunoassay has been developed which facilitates discrimination between canned whole sardine (Sardina pilchardus Walbaum) and other fish species (Pacific pilchard, mackerel, herring, sild and anchovy) that may be substituted for it in the canned product. The non‐competitive indirect ELISA utilizes an antiserum raised against a crude water‐soluble extract of canned sardine. Appropriate antiserum specificity was ensured by using extracts of those fish with which cross‐reactivity was undesirable, to achieve post‐production ‘blocking’ of unwanted cross reactions. This assay will be of value in upholding EC and UK law on the composition and labelling requirements of canned sardine products and provides a basis for the development of a rapid test format.