Department of Physical Chemistry, India.n Association for the Cultivation of Science, Jadavpur, Calcutta.-700 032 Manuscript received 14 May 1980, revised 14 July 1981, accepted 26 February 1989 Polyethylene, though quite insoluble in any single solvent at near room temperatare was earlier found to dissolve in a mixture of two non-solvents. A few such co- solvent pairs, including some new ones, have been studied in details with respect to cloud temperature and the existence of optimum solvent composition as judged by a maximum in intrinsic viscosity. The failure of Gee's criterion for cosolvency has been pointed out. The results have also been discussed, with only partial success, with respect to an equation derived by Deb and Palit, based on the thermodynamic approach of Scott. Probably, some kind of specific interaction and structure formation play an important role in such cosolvency.