Recombinant immunotoxin (RIT) contains the Fv portion of the antibody fused to the truncated form of toxin and are ongoing in clinical trials for cancer therapy. To obtain high yields of products, RITs are produced in Escherichia coli (E. coli ). As the endotoxin came from E. coli cells and is harmful to animals, it is important to produce the RITs with low endotoxin. This section describes the protocols to produce RITs containing low level of endotoxins.