The agreement gives Ipsos the option to increase its stake in the firm, which is the third-largest survey-based research firm in the Czech and Slovak markets, to 66% in 2009.
Pierre le Manh, Ipsos Europe chief executive officer, said: "Tambor will strengthen an already primary position in the region, giving us a significant presence in one of the last key markets in central eastern Europe where we needed to support our clients.
"The company, which has a strong reputation for innovation and client service, works with many of our global key accounts."
Tambor was launched in 1992 and covers qualitative and quantative research focusing on FMCG, retail, financial services and pharmaceuticals.
Ipsos already operates in Russia, Hungary, Romania, Poland and the Ukraine, employing around 400 staff in the central eastern European region.
Shane Farrell, chief executive of Ipsos central eastern Europe, said: "We work with many of our key clients on a regional basis so with Tambor we will now be able to offer even greater consistency in cross regional research programs."
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