The dynamics of commensurate chromium alloys are produced by the fluctuations of a spin-density wave consisting of bound electron-hole pairs. For a commensurate alloy at any temperature, we find a transverse spin-wave (SW) mode with frequency \ensuremath{\omega}=cq and a longitudinal amplitude mode with dispersion \ensuremath{\omega}=2\ensuremath{\surd}${\mathrm{\ensuremath{\Delta}}}^{2}$+(cq${)}^{2}$/4, where c=${\mathit{v}}_{\mathit{F}}$/\ensuremath{\surd}3 is the SW mode velocity and 2\ensuremath{\Delta} is the energy required to break apart an electron-hole pair. Unlike in an itinerant ferromagnet, the SW and amplitude modes never intersect. Other fluctuations below the SW mode and above the amplitude mode are intrinsically damped in an itinerant antiferromagnet.