AbstractThe experimental difficulties are discussed, which occur in the determination of values for the composition heterogeneity parameters of copolymers by light scattering measurements. The following requirements must be satisfied to determine experimentally the exact values of the composition heterogeneity parameters on the basis of the theoretical equation. [i] The parent homopolymers must be soluble in at least three (or six) solvents with different refractive indices for binary (or ternary) copolymers. [ii] The difference of the refractive index increments of the parent homopolymers must be sufficiently large compared with the experimental errors. As the difference changes slightly with the refractive index of the solvent, the precise relation should be obtained between the differences and refractive indíces of the solvent. [iii] The copolymer sample must be heterogeneous enough in composition so that the apparent molecular weight changes markedly with solvent.