An insert of Clostridium tetani DNA corresponding to fragment C of tetanus toxin was amplified by PCR. This 1.4 kb fragment was cloned into the high‐expression vector pET32a, under control of the T7 promoter. Expression of this plasmid in Escherichia coli BL21(DE3) resulted in the production of a fusion protein (≈62 kDa) consisting of 112 amino acids of thioredoxin and ≈450 amino acids of fragment C. This fusion protein was recognized by anti‐tetanus toxoid antiserum in an ELISA and on immunoblots. The recombinant fragment‐C‐thioredoxin protein was purified significantly in one step by Ni2+‐chelate Sepharose, the final yield being ≈35 mg/l. Immunization of animals with the recombinant protein produced antibodies that were able to recognize the tetanus toxin. By using this gene‐fusion expression system we produced soluble fragment C of tetanus toxin in a high yield, preventing many problems inherent in the use of other expression systems that produce either insoluble fragment C in inclusion bodies, or a soluble form, but in low yield, using E. coli as the expression host.