  We report on a near-infrared, long-baseline interferometric search for
luminous companions to the star 51 Pegasi conducted with the Palomar Testbed
Interferometer. Our data is completely consistent with a single-star
hypothesis. We find no evidence to suggest a luminous companion to 51 Pegasi,
and can exclude a companion brighter than a $\Delta$K of 4.27 at the 99%
confidence level for the 4.2-day orbital period indicated by spectroscopic
measurements. This $\Delta$K corresponds to an upper limit in the companion
M$_K$ of 7.30, in turn implying a main-sequence companion mass less than 0.22
M$_{\sun}$.
