Abstract Complexation between tetrabutylammonium bromide, or oligomeric tetramethyl‐2,6‐ionene bromide ( 1 ), and high molecular weight poly(ethylene oxide) (PEO) was studied viscometrically, using the following media as solvents: water; 0,1 M aq. KCl; 2 M aq. KCl and 0,1 M aq. HCl. It was found that tetrabutylammonium bromide as well as the ionene 1 convert the initially linear η red vs. c POE relationships into bent and hunchbacked curves, thus suggesting the formation of water soluble complexes. In aqueous KCl and HCl solutions these complexes behave as typical polyelectrolytes. Contrary to cations of alkali metals, however, protons do not influence the linear η red vs. c POE relation, so that it is possible to determine intrinsic viscosities by use of 0,1 M aq. HCl as solvent. These viscosities are rising if the complexation between POE and ammonium salt is accomplished by the polyfunctional ionene. The increase of [η] depends on the unit mole ratio (u.m.r.) of the ionene to POE. With increasing unit mole ratio from 0 to 7 [η] increases from 9 up to 21 dl · g −1 . In water the complexation between one unit mole of POE and two unit moles of ionene 1 causes an increase of the reduced viscosity η red from 11,2 up to 80,2 dl · g −1 .