  Magnetic monopoles are predicted in various unified gauge models and could be
produced at intermediate mass scales. Their detection in a neutrino telescope
is facilitated by the large amount of light emitted compared to that from
muons. This paper reports on a search for upgoing relativistic magnetic
monopoles with the ANTARES neutrino telescope using a data set of 116 days of
live time taken from December 2007 to December 2008. The one observed event is
consistent with the expected atmospheric neutrino and muon background, leading
to a 90% C.L. upper limit on the monopole flux between 1.3E-17 and 8.9E-17
cm-2.s-1.sr-1 for monopoles with velocity beta greater than 0.625.
