A synthetic gene encoding the He (binding) domain of Clostridium botulinum neurotoxin F (FHc) was expressed in Escherichia coli fused to maltose binding protein (MBP). The purified MBP-FHc and FHc isolated after removal of MBP were evaluated in mice for their ability to protect against toxin challenge. Balb/c mice developed a protective immune response following administration of either protein via the intraperitoneal or intramuscular routes. A comparison of antibody titres and protection following single and multiple vaccinations and the effects of dosage are shown. The long term protection afforded by the vaccines was also investigated. Ten months following vaccination mice were still protected when challenged with 10(4) MLD50 doses of botulinum toxin F. Crown Copyright (C) 2000 Published by Elsevier Science Ltd. All rights reserved.