Twelve commercial artificial tear solutions and a newly developed one were evaluated as to their effect on tear film breakup time (BUT) in ten normal subjects. Instillation of one drop of these solutions altered the BUT in such a way that serial BUT measurements could be used as an index of retention time. Results demonstrated significantly longer retention time for three related products (Adapt, Adapette, and Adsorbotear) and a newly developed product (Alcon 0413) [Tears Naturale (Alcon TM)]. This method appears to be an accurate nonirritative way of assessing retention time of tear substitute/vehicles and demonstrate values much longer than previously reported by other methods.