The review aims to consolidate the £80 million account into one agency and follows the merger of Mars and Wrigley, which took effect in October 2008.
The UK review follows Mars-Wrigley's appointment of Publicis Groupe-owned MediaVest to its media planning and buying account in the US.
ZenithOptimedia handles media buying across Mars' confectionery, petcare and food ranges with brands including Snickers, Pedigree and Uncle Ben's.
The £10 million Wrigley media buying account, handled by MediaCom, includes brands such as Juicyfruit and Airwaves.
