Constraining the mass of the Galaxy at large radii remains a difficult problem. Available data are still rather scarce, and orbits of even a few objects at large radii can have a large impact. We propose to obtain proper motions for the two satellites Leo I and Leo II, which orbit the Galaxy at about 200 kpc. Together with the radial velcoities of these glaaxies, which are well known, the proper motions allow space velocities ot be consructed: these can remove signifiicant uncertainty in the Galactic mass models, and in particular settle the vexed question of whether or not Leo I is gravitationally bound to the Galaxy. The proper motion of Leo I is addressed in a companion archival proposal; here we address the WFPC2 imagery of Leo II.

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