An advertising guru and his female co-worker who were called "the mad dwarf" and a "nympho schizo" by a colleague in an internet blog are suing for libel damages in the High Court.
Martin Sorrell and Daniela Weber - the chief executive of WPP and the chief operating officer of the company's Italian division respectively -allege the comments were part of a "vicious" internet campaign against them.
The court action has been brought against Marco Benatti and Marco Tinelli of Italian advertising agency Fullsix, who it is claimed made the remarks after Mr Benatti was fired by Mr Sorrell from his consultancy as manager of WPP in Italy.
It is alleged by Mr Sorrell that, after a threatening phone call from Mr Benatti's lawyer, the comments appeared on an internet blog in 2006 in what Mr Sorrel describes as an attempt to "undermine not only my professional reputation and career from its very beginnings, but also, probably in a more fundamental way my personal reputation ".
Both defendants deny responsibility for the comments, claiming that they had insufficient technical knowledge of internet blogs to have been able to post the remarks online.