The generation of monoclonal antibody (mAb) against marine toxins can serve as a valuable probe to detect this kind of compounds by immunological methods. However, traditional approaches to mAb generation usually need a comparative large quantity of standard substance (more than 400 microg mouse(-1)), and a comparative long immunization period (more than 6 weeks). Here we report a simple, inexpensive and fast protocol for the generation of monoclonal antibody probe specific for domoic acid (DA). In the method, lymph node cells were harvested from the Balb/C mice of hind footpad injection and fused with murine myeloma cells SP2/0 for hybridoma generation. This method for the preparation of mAb for DA has two main advantages: (a) there is no need for large-scale expensive antigen (only 70 microg antigen for one mouse); (b) immunization protocol can be accomplished within 16 days. Some characteristics of the mAb were studied and a direct competitive ELISA for the detection of DA using the mAb as a probe was developed. The detection limit was 0.41 ng well(-1) in phosphate buffered saline (PBS) and 0.53 ng well(-1) in blue mussel Mytilus edulis. The recoveries of DA from mussel and PBS buffer were from 94.8% to 105.1% and from 96.2% to 103.7%, respectively. Thus, the newly developed direct competitive ELISA using the mAb appears to be a reliable and useful method for monitoring of DA in shellfish (228 words).