A tier scheme is proposed for the assessment of ocular tolerance as part of the safety evaluation of materials. The scheme has four stages: (1) physico-chemical characterization, (2) an in vitro cytotoxicity study, (3) a dermal tolerance study in rabbits and (4) initial and confirmatory ocular tolerance studies in rabbits. The assessment may be terminated at any of the stages, including during the course of the final stage. This tier system appears to provide a considered and careful approach to the requirement to assess the ocular tolerance of those materials for which conventional animal tests are not essential.