This Motown-inspired song was written and produced by The Bee Gees: Barry, Robin and Maurice Gibb. Barry Gibb says in 1000 UK #1 Hits
by Jon Kutner and Spencer Leigh, "'Chain Reaction' was never originally meant to be on the album. It was the last song we cut. We'd done the whole album and Diana said, 'Well, we still need one more song from somewhere.' We had 'Chain Reaction' all along but didn't have the nerve to play it to her because it was so Motown-ish that we were scared she wouldn't go back there. Robin Gibb persuaded her by saying, 'We think it's time you did something that you would have done with The Supremes and not just Diana Ross.' Once Diana had recorded it, she sat down and heard the playback and realized it was a credible tribute to the past."