  We discuss here a limit on the maximum brightness temperature achievable for
an incoherent synchrotron radio source. This limit, commonly referred to in the
literature as an inverse Compton limit, prescribes that the brightness
temperature for an incoherent synchrotron radio source may not exceed ~10^{12}
K, a fact known from observations. However one gets a somewhat tighter limit on
the brightness temperatures, T_{b}~10^{11.5} K, independent of the inverse
Compton effects, if one employs the condition of equipartition of energy in
magnetic fields and relativistic particles in a synchrotron radio source. Pros
and cons of the two brightness temperature limits are discussed.
