This paper reports a study of the solvent role on complexation in systems composed by a polyacid and a polybase. Complexation has been found in water, n-alcohols, ethers and acetone, depending on the chosen polymer pair and temperature. The temperature at which the transition from a biphasic system to homogeneous solution occurs, has been employed as a measure of the relative stability of the complex. In general, complexes with bulky side groups are less stable than those with small ones. The influence of solvophobic and hydrophobic interactions has been discussed. The stability of complexes in ethers shows a marked dependence on the aliphatic character of the polymeric system, showing a complexing character similar to that of n-alcohols for the polymer systems with lower aliphatic character. Acetone is the most complexing solvent, probably due to its lower competing ability. Finally, it has been found that the relative stability of complexes with poly(ethyloxazoline) (compared with those with poly(N,N-dimethylacrylamide)) increases with the size of the side group of the poly(mono n-alkyl itaconate). (C) 1997 Elsevier Science Ltd.