Altherr had his contract purchased from Triple-A Syracuse on Saturday.
Altherr is back with the Mets to replace the injured Dominic Smith (foot), who was placed on the injured list Saturday. The 28-year-old Altherr is slashing just .050/.095/.150 in 29 games (42 plate appearances) this season, so he'll likely be limited to a bench role during his time with the big club.