We previously reported the production of a fused snake neurotoxin composed of protein A and erabutoxin a in E. coli. The hybrid had much lower toxicity and affinity for the acetylcholine nicotinic receptor than natural erabutoxin. By treating the hybrid with cyanogen bromide we generated a toxin which was purified in a single step by RP-HPLC. This compound, produced in a good yield, recovered all properties of native erabutoxin a, implying that the lower toxic activities of the hybrid were due to the bulky protein A and not to an incorrect folding of the toxin. This work serves as a basis for future studies of toxin-receptor interactions using engineered toxin mutants.