We study aqueous solutions of maleic acid-vinyl acetate alternating copolymers in a wide range of polymer C and salt C-s concentrations by means of static and dynamic light scattering. Depending on C and C-s, the decay of the autocorrelation function of the scattered electric field is characterized by one or two modes of relaxation. This feature allows one to define the dilute and semi-dilute regimes in a diagram C-C-s. The fast mode of relaxation has the usual behavior reported for polyelectrolyte solutions. The slow mode of relaxation can be linked with the occurrence of chain aggregation. The proposed driving force for the aggregation is the lactonization of the monomers that decreases their solubility in water. Ultimately a phase separation occurs after a time of several weeks that depends on C and C-s. (C) 2000 Elsevier Science Ltd. All rights reserved.