The anomalous wide-angle X-ray scattering (AWAXS) technique has been u
sed for the determination of the total and differential structure fact
ors of amorphous ternary Co79-xErxB21 alloys. Three melt-spun ribbons
with x = 3.9, 7.5 and 9.5 at.% have been investigated. The experiment
at the Co K edge has allowed us to extract the total and differential
structure factor for each concentration and to calculate the different
ial distribution of pairs around cobalt. A preliminary analysis of the
results shows that an important modification of the local order of Co
atoms takes place in alloys with more than 7.5 at.% Er.