Research on cationic surfactant drag-reducing additives has grown in recent years because of their repairability after shear degradation, making them suitable for potential applications in recirculation flows such as district heating and district cooling systems. Substantial differences between their flow behaviors and those of high-polymer, drag-reducing additives have been found. These include the influence of preshearing, the effect of mechanical shear on degradation, the influence of tube diameter, maximum drag-reduction effectiveness, and the shape of their mean velocity profiles. Examples of these different flow behaviors are described. The differences suggest that the mechanisms for causing drag reduction may be different for the two types of additives.