Polyclonal antisera for the immunological detection ofBotrytis alliiwere raised from cell wall, cytoplasmic and surface plate washings of two isolates of the pathogen. These antisera were used to develop an indirect ELISA for the detection of latentB. alliiinfection in stored onion bulbs. The antisera did not react with healthy onion tissue and showed only minimal recognition of fungi from other genera. Some cross reactivity was observed withB. cinereabut not with otherBotrytisspecies tested. In many instances following infection, fungal antigen could be detected earlier by ELISA than by direct plating. In tests on bulbs from a commercial store, the level ofB. alliiinfection was found to be 3.3% by both ELISA and direct plating, but this result was achieved 7 days sooner by ELISA.