The underside of a flask found in a government research laboratory.

Purity Control was the name for a top secret government project, under the control of the Syndicate, to create alien-human hybrids. The project initially centered around using gene therapy using alien DNA to cure terminally-ill cancer patients. These patients quickly recovered, developed super-human strength and the ability to breath underwater. These patients' blood/bloodgas is incredibly toxic to humans and is green in color.

After a patient, Dr. William Secare, escaped into the population certain sections of the project were quickly shutdown; all evidence and any knowledgeable person(s) were destroyed by Syndicate Operatives. Special Agent Dana Scully gained access to a sample (where "Purity Control" was the password) of alien DNA which Deep Throat then used it to negotiate the safe return of Agent Mulder (TXF: "The Erlenmeyer Flask").

The material from the sample was also used in a large scale test on livestock and humans in a small beef farming town in Wisconsin (TXF: "Red Museum").

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