The accuracy of the quasi-chemical approximation used in the theoretical treatment of a lattice model for solutions in which cooperative orientation of molecules takes place is examined. The quasi-chemical method of Guggenheim and the modified quasi-chemical method of Kikuchi are used to find higher approximations. It is found that the quasi-chemical approximation for pairs is satisfactory for lattices which are not closepacked, though it may be seriously in error for closepacked lattices.