This is...
Where one word leads to another!
And the star of Chain Reaction...
Bill Cullen!
Broadcast History
Airdates: January 14, 1980-June 20, 1980, NBC
Host: Bill Cullen
Substitute Host: Geoff Edwards (Two Weeks)
Announcer: Johnny Gilbert
Origination: NBC Studios 2 and 4, Burbank
Packager: Bob Stewart Productions
Main Game
Chain Reaction was
played by two teams, with one contestant and two celebrities. The object was for
the teams to fill in a "chain" of words.
An example chain is shown on the left. It starts with fault. Fault obviously
leads to earthquake. An earthquake is a disaster. A disaster was the sinking of
the Titanic. The Titanic hit an iceberg. Iceberg's are cold. To quit something,
you quit cold turkey. And turkey is usually something you have for dinner.
To
start each chain, the top and bottom words were revealed.
The object was for the two teams to fill in the remaining six in between.
When the first team got control, they could ask for a letter either below the
first word, or above the last word. If they guessed the word of the letter they
asked for correctly, they received one point for every letter in the word they
guessed and keep control, unless there's a "+" sign in that box, which
means they got double the point value.
If they guessed incorrectly, the opposing team gets a chance. Only one player
per team played at a time (shown by red lights in front of them). 
First
team to reach 50 points wins the game
and goes to the bonus round.
Bonus Round
The
object of the bonus round remained the same throughout, but the scoring was
different at numerous times.
The object was for the two celebrities to convey answers, seen in their secret
screens, by formulating a question to the contestant by adding one word at a
time. To finish the question, they'd hit a bell. If a player used more than one
word or they made an incorrect answer, they'd hear the cuckoo sound effect (more
famous on the Pyramid series), and they'd go to the next word. In the first
scoring format, 60 seconds was
given to get 8 correct answers. 
The
player started with $1, and for each correct answer, won a half zero (a full
zero meaning they'd win whatever the number was), until they reached $10,000.
This was scrapped quickly, after the first week, especially after the laughable
first bonus round, where a player won $10.
The second bonus was blamed as being too easy. This time, the first correct
answer was worth $1, and for each correct answer, a zero was added until they
reached $1,000.
After that, each correct answer was worth $1,000, until they reached $5,000,
when the 9th correct answer was worth $10,000. The third format had the player
trying to get 10 correct answers in 90 seconds, with each worth $100, until the
10th for $10,000. 
And
finally, the fourth format was 9 correct answers in 90 seconds with $100 awarded
for each correct answer, with the 9th worth $10,000.
Pilot
The
Chain Reaction pilot was produced in October 1979. The format was very similar
with what ended up coming to air. Two teams consisting of a celebrity (Joyce
Bulifant and Nipsey Russell served on the pilot) and a married couple competing,
with 
only
one member of the couple competing on a chain. The scoring was the same, except
the last word was always worth double. 50 points won the game.
There
some minor set differences, as the board looked different, and actually rotated
for each chain, making for an oddly
figured chain at times.
That chain looks familiar doesn't it?
In the bonus round, yet another
scoring change! The bonus round was known as the Instant Reaction. This time,
the team had 60 seconds to get 7 correct answers. They started with $.01, and 
for
each correct answer, the decimal point moved to the right, 
which
meant a possible win of $100,000!
Facts
-Geoff Edwards guest hosted two weeks worth of shows for Bill Cullen, who was over on another NBC game show, Password Plus, guest hosting for an ill Allen Ludden. Geoff would later host a cheaper, non-celebrity version (now you know why it's not covered) of Chain Reaction on the USA cable network (taped in Montreal) from 1986-1991. Canadian country singer Blake Emmons was also a host of that version early on.
-The bonus game later became an entire game show in itself, Go!, which aired on NBC in 1983-1984. It was earlier tried out on a pilot called Get Rich Quick.
-Reruns aired on the CBN and USA (before the new version started) cable networks during the 1980s. Game Show Network reran the show during it's "Dark Period" (where they lost the rights to many Goodson-Todman shows and had to scramble to fill it's schedule) in 1997-1998.