  We present preliminary results of an ongoing survey to probe the physical
nature of a sample of open clusters (POCRs, Bica et al. 2001) believed to be in
an advanced stage of dynamical evolution. This kind of object is very important
to constrain dynamical $N$-body models of clusters evolution and dissolution,
and to understand the formation of the Galactic field stars population.
Moreover they might represent what remains of much larger old clusters, which
are of paramount importance to probe the early stages of the Galactic disk
evolution. In this paper we present our results for NGC 1901.
