  A new observing mode for the Palomar Testbed Interferometer was developed
in2002-2003 which enables differential astrometry at the level of 20
micro-arcseconds for binary systems with separations of several hundred
milli-arcseconds (mas). This phase-referenced mode is the basis of the Palomar
High-precision Astrometric Search for Exoplanet Systems (PHASES), a search for
giant planets orbiting either the primary or secondary star in fifty binary
systems. We present the first science results from the PHASES search. The
properties of the stars comprising binary systems are determined to high
precision. The mutual inclinations of several hierarchical triple star systems
have been determined. We will present upper limits constraining the the
existence of giant planets in a few of the target systems.
