Gerald Perry Finnerman was encouraged to be creative in choosing dramatic lighting and camera angles. Robert H. Justman recalled that he said to Finnerman, "We're all in outer space, Jerry, and we're in color. NBC claims to be the first full-color network, so let's prove it for them. When you light the sets, throw wild colors in - magenta, red, green, any color you can find - especially behind the actors when they're in a close shot. Be dramatic. In fact, go overboard. Backlight the women and make them more beautiful. Take some chances. Nobody can tell you that's not the way the future will look. How can they? They ain't been there yet." Bob Justman was very pleased with the final results in this episode. He stated, "Guest stars Karen Steele, Maggie Thrett, and Susan Denberg, good-looking in real life, looked even more radiantly lovely and ravishing as they worked their magic upon Captain Kirk and crew - after Jerry worked his magic upon the three actresses."
During the very early pre-production days of "Star Trek - The Next Generation" (1987-1994), Gene Roddenberry proposed to have Roger C. Carmel return and make a guest appearance, possibly as Harry Mudd, in order to provide an extra link with the original series. However, nothing came of this as Carmel died unexpectedly at the relatively young age of 54, several months before the pilot show was filmed.
Susan Denberg (playing Magda Kovacs) appeared in this episode two months after revealing herself as the Miss August 1966 centerfold in Playboy.
This and Where No Man Has Gone Before (1966) are the only episodes where the crystals that power the Enterprise's engines are called "lithium." Throughout the rest of the series, the crystals are called "dilithium."
The velour uniforms used in this episode had shrunk since they were first used in The Corbomite Maneuver (1966). According to Robert H. Justman and Herbert F. Solow's book "Inside Star Trek: The Real Story," the velour uniforms shrank every time they were cleaned. The actors' union requirements specified that the costumes had to be cleaned daily.