The genus Clostridium contains some of the most toxic bacteria known to man (e.g., Clostridium tetani, Clostridium botulinum) as well as solvent-producing organisms of biotechnological interest (e.g., Clostridium acetobutylicum). Developments within the areas of plasmid vector construction and plasmid delivery methodology now provide the opportunity for applying recombinant DNA technology to this important group of bacteria.