Clostridium botulinum produces several powerful neuroparalytic toxins which, although rare in food-poisoning instances, are generally fatal. A considerable amount of effort has therefore been made by the food industry to ensure that food treatment processes adequate to prevent growth and toxin production by Cl. botulinum. Laboratory mice and guinea-pigs are presently used extensively both for the assay of botulinum toxins and for the development and assessment of vaccines used to protect laboratory workers. An amplified ELISA, using a monoclonal antibody, has been developed for botulinum type A toxin with a sensitivity similar to that of the mouse acute toxicity test. The immunoassay has been found to be applicable to the detection of toxin in foodstuffs and could replace the currently used mouse bioassay in many laboratories. Immunoassays have also been developed for the detection of antibodies to botulinum toxins. A preliminary study has shown that antibody titres to botulinum types A and B toxins in sera taken from immunised personnel, as measured by ELISA, showed limited correlation with those measured by the toxin neutralisation test in mice. A more extensive study should determine whether the latter test can be replaced by the ELISA.