  We study the drag force and diffusion coefficient with respect to a moving
heavy quark in a D-instanton background, which corresponds to the Yang-Mills
theory in the deconfining, high-temperature phase. It is shown that the
presence of the D-instanton density tends to increase the drag force and
decrease the diffusion coefficient, reverse to the effects of the velocity and
the temperature. Moreover, the inclusion of the D-instanton density makes the
medium less viscous.
