The present invention provides processes for determining the molecular weight of glatiramer acetate and other copolymers. The present invention further provides a plurality of molecular weight markers for determining the molecular weight of glatiramer acetate and other copolymers which display linear relationships between molar ellipticity and molecular weight, and between retention time and the log of the molecular weight. The molecular weight markers also optimally demonstrate biological activity similar to glatiramer acetate or corresponding copolymers and can be used for treating or preventing various immune diseases. In addition, the subject invention provides pharmaceutical compositions for the treatment of immune diseases comprising a polypeptide having an identified molecular weight and an amino acid composition corresponding to glatiramer acetate or a terpolymer.