Unit Ei 1644 (), also known as Unit 1644, was one of the water purification centers established underneath the Epidemic Prevention and Water Purification Department. An anonymous "researcher" who claims he was attached to Unit 1644 says that it regularly carried out human vivisections as well as infecting humans with cholera, typhus, and bubonic plague. According to Hal Gold, who included this report in the book Unit 731 - Testimony in 1996, this "researcher" said he would soon publish his complete testimony, but no such testimony has yet been released.