  We present a theoretical analysis of the appearance of entanglement in
non-interacting mesoscopic structures. Our setup involves two oppositely
polarized sources injecting electrons of opposite spin into the two incoming
leads. The mixing of these polarized streams in an ideal four-channel beam
splitter produces two outgoing streams with particular tunable correlations. A
Bell inequality test involving cross-correlated spin-currents in opposite leads
signals the presence of spin-entanglement between particles propagating in
different leads. We identify the role of fermionic statistics and projective
measurement in the generation of these spin-entangled electrons.
