We present ab-initio calculations for the electronic structure of 3d,
4d and 5d transition-metal impurities at the (001) surface of Cu and A
g and determine the surface enhancement of the local moments. For 3d i
mpurities we find a sizable enhancement of the local moments, being mo
st important for V and Cr. Large local moments are obtained for 4d and
5d impurities which are in general non-magnetic in the bulk. Some of
the adatoms (Nb, Mo, Tc, W, Re) on Ag (001) have ''giant'' magnetic mo
ments between 3 and 4 mu(B).