3 Pauillac, S. Sasaki, M. Naar, J. Inoue, A. Murata, M. Tachibana, K. Chinain, M. Legrand, A-M. 1998 In: Harmful Algae. Reguera B, Blanco J, Fernandez ML, Wyatt T (Eds). Intergovernmental Oceanographic Commission of UNESCO, Xunta de Galicia (Spain), pp 563-566 1998 A conjugate of JKLM ring fragment, a carboxylic derivative of the right-hand tetracyclic terminus portion of CTX-1B, the most potent ciguatoxin, with two carrier proteins has been synthesized. Hapten-carrier amide linkages were promoted using the N-hydroxysuccinimide ester of the carboxylic fragment in the presence of a water soluble carbodiimide according to standard condensation procedure. Bovine serum albumin (BSA) and ovalbumin (OVA) were respectively used for i.p. immunization of two BALB/c mice and antibody screening. Titres of both antisera as determined in an end-point titration ELISA format were found around 1/16,000.A competitive inhibition ELISA was used to assess the specificity of mice polyclonal antibodies (PAbs). PAbs did not significantly cross-react with PbTx-3 or nigericin but did show 133% cross-reaction with CTX-1B. The lower limit of accurate JKLM ring fragment and CTX-1B determinations in competitive ELISA was respectively 50 and 30 picomoles. It was concluded that the competitive ELISA described herein could be further improved to enable direct quantitation of ciguatoxins (CTXs) in crude fish extracts. Moreover 29 monoclonal antibodies to JKLM have been produced but only one seemed to react exclusively with JKLM ring fragment.