A fluid sampling system comprising a housing, a first pump means for withdrawing at least one fluid sample from a first sample site, means for returning at least part of the at one fluid sample to a second sample site, transferring means for transferring at least one volume of the at least one first fluid to a sampling means, second pump means for providing at least one active substance, at least one connection to a reservoir containing the at least one active substance, and at least one energy source for driving at least the first and second pump means.
