The neurotoxin gene from Clostridium botulinum type G was cloned as a series of overlapping DNA fragments generated using polymerase chain reaction (PCR) technology and primers designed to conserved regions of published botulinal toxin (BoNT) sequences. The 5'-end of the gene was obtained using a primer based on a conserved region of the nontoxic-nonhaemagglutinin gene lying upstream of the toxin gene. Translation of the nucleotide sequence derived from the cloned PCR fragments demonstrated that the gene encodes a protein of 1297 amino acid residues (rmm 149, 147). Comparative alignment of the determined BoNT/G sequence with those of other clostridial neurotoxins revealed highest sequence relatedness (approx. 58% amino acid identity) with BoNT/B of proteolytic and non-proteolytic C. botulinum. Tetanus toxin (TeTx) and other BoNT types revealed lower levels of relatedness with BoNT/G (approximate range 35-42% amino acid identity).