  We consider a special class of dimension-six operators which are assumed to
be induced by some new physics with typical scales of order \Lambda. This
special class are the operators with two quarks which can mediate transitions
between quark flavours. We show that under quite general assumptions the effect
of these operators can be parametrised in terms of six parameters, leading to a
modification of the (at tree level flavour diagonal) neutral currents and to an
``effective CKM matrix'' for the charged currents, which is not necessarily
unitary any more. The effects of these operators on charged and neutral
currents are studied.
