Morphological and powder rheological parameters of phenobarbitone and alpha-methyldopa were tested. The habits of the crystals were investigated by scanning electron microscopy (SEM). Particle size distribution was tested with an image analysis system. The rearrangement factors (k), the compactibility and the cohesiveness of the crystals were calculated from the loose and tapped volumes of the drugs. It was concluded that the habits of the tested drugs were different, as were the particle sizes and the particle size distributions. These properties influence the rearrangement of the particles. Finally, it was established that the powder rheological parameters of phenobarbitone are better than those of alpha-methyldopa.