Stability of aqueous and nonaqueous silicon nitride suspensions prepared in an ultrasonic bath was compared with the stability of analogous suspensions prepared by an ultrasonic disrupter. The settling velocities of the nanometric, laser driven silicon nitride powder were evaluated up to 24 h on the basis of screening sedimentation tests. It was shown that the stability of deflocculated suspensions (prepared by ultrasonic disrupter) can be predicted by the DLVO theory, whilst the stability of more agglomerated suspensions (prepared by ultrasonic bath) is to be related to the dielectric constant of the applied dispersion media.