The episode first aired in the United States on January 28, 2011 to an estimated 4.57 million viewers, making it the highest rated program of the night.

The Fringe division visits a secured Massive Dynamic facility where the prime universe's version of the doomsday device, believed to be an artifact of the "First People", has been assembled.

They are aware that before her departure, Fauxlivia (Anna Torv)—Olivia's parallel universe doppelgänger—stole one component of the unit, possibly its power source as they cannot find any other way to engage the device.

Walter enters his room, finding printed pages of Fauxlivia's notes including the circled names of the shapeshifters, those that Olivia just identified.

[3] The episode featured one-time guest roles by actors Charles Parnell as Dr. James Falcon and Sean Campbell as Zach Alpert.

[11][13] It was the highest-rated program of the night, as it tied with NBC's Dateline, but its ratings were not enough to prevent the Fox network from placing fourth in total viewers.

Ken Tucker from Entertainment Weekly enjoyed the scenes set at Massive Dynamic, and thought the episode did a good job tricking the audience into thinking Peter was not responsible for the shapeshifter killings.

[17] SFScope contributor Sarah Stegall believed the episode "got us quickly back on track after last week's lackluster tale," and called the killer revelation the greatest shock she has received on the series thus far.

[1] She continued that one of her favorite parts of the Peter-as-a-killer arc is being able to watch the emotional setbacks he is facing as a result of Fauxlivia's betrayal; she called it "good characterization, and excellent acting".

[1] IGN columnist Ramsey Isler praised the writing staff because "just when you think they might be stuck in old habits, they come up with new ideas and put a whole new perspective on old storylines and characters.

"[7] Isler continued that while "'Reciprocity'" isn't the most groundbreaking episode in the series, it does try a number of new ideas, and it gives us one big new plot point that could change the tone of the rest of the season.