Proutiere's theory of mol. wt. (M) detn. by Rayleigh scattering has been tested on surfactants in soln., and it has been compared to the classical Carr-Zimm (CZ) method. Both methods make use of time-averaged scattering intensity, refractive index, and d. measurements. Monoethers of poly(ethylene glycol) samples have been studied in the range 0.33-4.67 kg/mol of M. Under those conditions, it has been shown that Proutiere's method leads to a far better agreement with formula wt. (M) values than the CZ method because Proutiere theory takes into account the specific mean polarizability of the solvent and deriv. of the soln. d. with respect to the solute mass concn., which is counter to CZ theory. [on SciFinder (R)]