Ethyl(hydroxyethyl)cellulose (EHEC) forms true molecular solutions in 10 mM aqueous solution NaCl at concentrations equal or less than 0.1%. Less hydrophilic EHEC forms true molecular solution also in methanol/10 mM aqueous NaCl(1:I, v/v) mixture. An associative clustering was observed in this solvent mixture in the case of a more hydrophilic EHEC derivative. The amount and size of clusters increased with EHEC sample concentration. Repulsive forces related to some minute charge of EHEC, evidenced by ion-exclusion chromatography in the absence of salt in the methanol/water (1:1, v/v) mobile phase, became operative in clustering solution without salt; both the amount and size of clusters decreased. EHEC contains a low amount of particle impurities. The light-scattering signal related to these impurities may be misinterpreted as an aggregation when the solutions are not properly filtered.