The Chandrasekhar dynamical friction and diffusion coefficients
are derived for a massive binary that moves against a uniform
background of stars.
The random impulses exerted on the binary's center of mass by the
field stars are greater than those exerted on a point particle due
to super-elastic scattering.
The frictional force acting on the binary is less than that
acting on a point particle due to randomization of the trajectories of
field stars that pass near the binary.
Both effects tend to increase the random motion of
a binary compared to that of a point mass.
If the maximum effective impact parameter for gravitational
encounters is comparable to the radius of gravitational influence
of the binary,
its Brownian motion can be increased by a modest factor
compared with that of a single particle.