Dry eye patients present with instability of the precorneal tear film which breaks up much earlier than normally. The instability of the precorneal tear film leads to dry eye symptoms such as the sensation of sand in the eye, recurrent blurred vision, itching, smartness, and the sensation of dryness. The stability of the precorneal tear film can be evaluated by the break-up-time test (BUT). The aim of treatment of dry eye is to increase the precorneal tear film stability. Tear substitutes are the most frequent medication for dry eye patients, who request life-long treatment. Therefore, we estimated the influence of tear substitutes on the precorneal tear film stability. The influence of unpreserved artificial tear substitute containing 0.1% sodium hyaluronate (Healon 0.1%) was compared with that of 7 different available tear substitute preparations containing preservatives. The results of the present study show that Healon 0.1% has the best influence on the precorneal tear film stability. These data were found to be independent of the viscosity property of Healon 0.1%.