  We have studied the photometric properties of four fields around the
high-redshift quasar pairs QP1310+0007, QP1355-0032, QP0110-0219, and
QP0114-3140 at z ~ 1 with the aim of identifying large-scale structures- galaxy
clusters or groups- around them. This sample was observed with GMOS in Gemini
North and South telescopes in the g', r', i', and z' bands, and our photometry
is complete to a limiting magnitude of i' ~ 24 mag (corresponding to ~ M*_i' +
2 at the redshift of the pairs). Our analysis reveals that QP0110-0219 shows
very strong and QP1310+0007 and QP1355-0032 show some evidence for the presence
of rich galaxy clusters in direct vicinity of the pairs. On the other hand,
QP0114-3140 could be an isolated pair in a poor environment. This work suggest
that z ~ 1 quasar pairs are excellent tracers of high density environments and
this same technique may be useful to find clusters at higher redshifts.
