The purpose of this work was to map the entire recognition profile of the H chain of botulinum neurotoxin A (BoNT/A) by Abs in sera that have protective anti-BoNT/A Abs by the mouse protection assay (MPA) from cervical dystonia (CD) patients who had been treated with botulinum neurotoxin, serotype A (BOTOX). In previous studies we found that human anti-tetanus neurotoxin (TeNT) Abs cross-react with BoNT/A and BoNT/B. In the present work we devised an assay procedure for measuring specific anti-BoNT/A Abs in human sera by absorbing out or inhibiting the anti-TeNT Abs with TeNT before analyzing the sera for the anti-BoNT/A Abs. The sera were obtained from 28 CD patients who had become unresponsive to treatment with BoNT/A and the sera were found to protect mice against a lethal dose of BoNT/A. For localization of the Ab-binding regions on the H chain we employed a set of sixty, 19-residue synthetic peptides (except for peptide C31 which was 22 residues) that encompassed the entire H chain sequence 449-1296 and overlapped consecutively by five residues. The pattern of Ab recognition varied from patient to patient, but a very limited set of peptides were recognized by most of the patients. These were, in decreasing amounts of Ab binding, peptide N25 (H chain residues 785-803), C9/C10 (967-985/981-999), C31 (1275-1296), C15 (1051-1069), C20 (1121-1139), N16 (659-677), N22 (743-761), and N4 (491-509). But not every serum recognized all these peptides. The finding that the binding profile was not the same for all the patients is consistent with previous observations that immune responses to protein antigens are under genetic control and that the response to each epitope within a protein is under separate genetic control. Except for the region within C9/C10, the other regions either coincided (N16 and C31), or overlapped (N4, N22, N25, C15 and C20), with the recently mapped synaptosomes (snps)-binding regions on the H chain. The molecular and clinical implications of these findings are discussed.