AbstractIn macromolecular chemistry the concentrations normally used are such that the molecules are entangled because of their large dimensions. Only at high dilutions the average distance between the molecules is greater than their own dimensions. The dilution at which the molecules can begin to move independently is called “the critical concentration” and is obviously a function of the molecular weight. It has been debated at length if the properties of macromolecular solutions change markedly in the vicinity of the critical concentration. Conflicting evidence from experimental measurements can be found in the literature, particularly from viscosity data. Recent precision measurements show that viscosity anomalies observed around the critical concentration are due to an earlier unknown correction (öHRN's correction) caused by the adsorption of solute molecules on the wall of the capillary viscometer. Therefore precision viscometry gives no indication of critical concentration effects. Few highly accurate studies have been carried out by other methods, but at present none of these data (sedimentation, diffusion) indicates the existence of ciritcal concentration effects. This means that linear extrapolations to zero concentration can be performed without fear of a sudden change in slope when the critical concentration is passed. From the experimental point of view, the development of precision methods for macromolecular measurements at high dilutions in this connection will certainly lead to a better knowledge of polydispersity effects and molecular weight distributions ‐ measurements can now be carried out at concentrations low enough to make concentration dependent effects vanishingly