The Manster

 is a 1959 American science-fiction horror film. Shot in Japan, it was produced by George P. Breakston and directed by Breakston and Kenneth G. Crane from a screenplay by Walter J. Sheldon. Sheldon's script was based on Breakston's story which he originally titled "The Split". 
The film starred Peter Dyneley as a foreign correspondent in Japan who is given an experimental drug which causes an eye and eventually, a second head to grow from his shoulder. Tetsu Nakamura played the mad scientist, Dr. Suzuki, with Tamoko Takechi as his horribly mutated wife, Emiko.
Plot.
American foreign news correspondent Larry Stanford (Dyneley) has been working out of Japan for the last few years, to the detriment of his marriage. His last assignment before returning to his wife in the United States is an interview with the renowned but reclusive scientist Dr. Robert Suzuki (Tetsu Nakamura), who lives atop a volcanic mountain. During the brief interview, Dr. Suzuki amiably discusses his work on evolution caused by sporadic cosmic rays in the atmosphere, and professes that he has discovered a method for producing evolutionary change by chemical means. Suzuki serves Larry a drugged libation, causing him to fall into a deep sleep. Announcing to Tara (Terri Zimmern), his voluptuous assistant, that Larry is the perfect candidate for his latest evolutionary experiments, he injects an unknown substance into Larry's shoulder. Upon waking, Larry is oblivious to the true situation and accepts Suzuki's invitation to spend the next week vacationing with him around Japan. Over the next few days, Suzuki uses Tara as a beguiling distraction while conditioning Larry with mineral baths and copious amounts of alcohol, exacerbating the pain in Larry's shoulder.
Meanwhile, Larry's estranged wife (Jane Hylton) has traveled to Japan to bring him back home with her. When confronted, Larry refuses to leave his new life of women and carousing. After a few drinks that night, Larry examines his painful shoulder to discover that a large eyeball has grown at the spot of Dr. Suzuki's injection. Becoming aloof and solitary, Larry wanders Tokyo late at night. He murders a woman on the street, a Buddhist monk and a psychiatrist, while slowly changing form, culminating in his growing a second head. Seeking a cure, Larry climbs the volcano to Dr. Suzuki's laboratory where Suzuki has just informed Tara that Larry has become "an entirely new species" and beyond remedy. Entering the lab, Larry kills Suzuki and sets the building on fire as Tara flees. Larry splits into two completely separate bodies, bringing himself back to normal. The monstrous second body grabs Tara, and throws her into the volcano. As Larry's wife and the police arrive, he pushes the second body into the volcano. Larry, now cured, is taken away by the police, although it remains unclear how much moral or legal responsibility he has for his violent actions. The movie ends as Larry's wife and his friend discuss the good that remains in Larry.
Production.
"The Manster" was an American production filmed in Japan, using a mostly Japanese crew and a number of Japanese actors. "The Manster" was shot in English. The film had various working titles, including Nightmare and The Two-Headed Monster. It was photographed by David Mason and edited by Kenneth G. Crane. Shinpei Takagi handled the special effects, George Wyman played the titular monster and Hirooki Ogawa composed the soundtrack.
Release.
Lopert Pictures released "The Manster" in the United States on March 28, 1962 as a double feature with "Eyes Without a Face". In the United Kingdom, "The Manster" was released as The Split.
Sources state different release dates for the film. AllMovie states that the film was released in the United States on July 1, 1959. In his book "The Japanese Filmography", Stuart Galbraith IV wrote that the film was first released in Japan in 1961, followed by an American premiere on March 28, 1962. The American Film Institute also states that the film premiered in the United States in San Francisco on March 28, 1962, at a run time of 72 minutes.
The film was shown on "Elvira's Movie Macabre" and later released on DVD.
Reception.
In a contemporary review, the "Monthly Film Bulletin" reviewed a 67-minute version of "The Manster" titled "The Split". The review called the film to be "a pathetic pot-boiler", "never frightening" and an "incredibly far-fetched rehash of all the ingredients of the convention SF-horror film". The review criticized the fact that the second head of the character appears to only "bob up and down on the actor's raincoated shoulder, only visible in night scenes and never in close-up".
In a retrospective review, AllMovie film critic Hal Erickson wrote, ""Manster" is a favorite among campy horror aficionados and for good reason as it is both unintentionally funny and genuinely creepy...Wait till you see the climax, with the hero battling himself on the edge of a live volcano".