Soluble silicates represent a broad range of chemical substances, which, to meet EEC laws, must be classified and labelled to identify their toxicological hazards. The wide range of this type of substance which can be manufactured, and the potentially severe effects which can be produced in standard eye irritation tests, means that classification by standard animal procedures is undesirable. One of the most reliable in vitro assays for assessing eye irritation potential is the rabbit enucleated eye test. This procedure has been used to test a range of soluble sodium silicates to enable these materials to be classified for eye hazard. The experimental approach demonstrates an important example of how an in vitro procedure can be used to propose classification for materials in a reasonable, scientifically valid way, taking account of the nature of the potential hazards and the intrinsic limitations of the in vitro methods used.