The critical concentration, c*, at which overlapping between macromolecular chains occurs, has been studied using dynamic (viscometry) and static (light scattering) methods. With the same polymer-solvent system this critical concentration has a higher value when viscometry is used, compared to the concentration obtained when using a light scattering technique. This difference is attributed to an incipient decrease of the dimensions of the macromolecular coils above the critical concentration c**, which is observed only under dynamic conditions. Relationship between the critical concentration c* and both the intrinsic viscosity and the molecular weight of the polymers are proposed.