Masters and Johnson, played in the series by Michael Sheen and Lizzy Caplan, studied more than 10,000 orgasms in a decade-long experiment.
Masters, a fertility expert, sought the help of a photography expert to create a transparent dildo, mounted with a camera, to observe for the first time ever the inside of a woman's vagina during penetration and orgasm.
The research cleared up questions doctors had just been guessing at -- often incorrectly.
At a session with the Television Critics Association Tuesday, Sheen said "I never thought I’d get used to having a naked woman in front of me masturbating with a glass dildo…but I actually broke that barrier on the show."
Indeed, the series shows a lot of sex. Not only in the lab with electrodes, monitors and cameras, but also in the protagonists' tangled personal lives.
One critic wondered whether it was difficult for the actors to do so many sex scenes, and whether they were "always excited, and did any of you ever go to Catholic school and did it affect your performance?"
Caplan credits Masters and Johnson with helping women accept their sexual curiosity and behaviors as normal, "not dirty … Before Masters and Johnson, no one was telling women that. It was always their fault -- and that’s some [expletive]."
Caplan also told critics that she learned during filming that "people’s masturbatory techniques are lot like snowflakes." Sheen joked back, "Cold, and you end up wet."
The series is based on Thomas Maier’s book "Masters Of Sex: The Life & Times Of William Masters And Virginia Johnson, The Couple Who Taught America How To Love," which came out in 2009, but which has just been released in a new edition.
Masters died in 2001, but Maier was able to interview Johnson extensively. Sadly, Johnson died just last week without ever seeing footage of the show.