Played by series stars Nathan Fillion and Stana Katic, the pair locked lips in a scene filmed outside a downtown warehouse late Thursday for a January episode.
As "Castle" fans know, the show's weekly whodunits share equal weight with the will-they-or-won't-they romance conundrum for the lead characters.
Castle is a best-selling mystery writer and single dad who is an eager consultant with the New York Police Department. Beckett is the no-nonsense detective ordered to work with him. Their growing sexual tension - and banter - is reminiscent of the 1980s "Moonlighting" mystery series with Sybil Shepherd and Bruce Willis.
Sooner or later, however, TV viewers demand results from such chemistry lessons.
"Castle" executive producer-creator Andrew W. Marlowe said Friday he's aware that many loyalists are rooting for Castle and Beckett to "take their relationship to the next level." The show couldn't hold off forever, Marlowe said.
But ratings can suffer when a lively mating dance turns to humdrum romance, so expect "Castle" to take it slow on the potential road to love.
The Castle-Beckett smooch comes during an episode about Beckett's long-frustrated effort to solve her mother's murder. There's more to the lingering embrace and kisses than passion, according to the script. The episode's January date has yet to be determined, ABC said.
"Castle" (10 p.m. ET Monday) has become a hit for the network, routinely landing in the top 20 in the Nielsen ratings and attracting more than 10 million viewers weekly in its third season. It has also inspired mystery novels published under Castle's name and featuring a fictional heroine, Detective Nikki Heat, based on the fictional Beckett.