Tear osmolarity and Rose Bengal staining were studied in a group of patients with keratoconjunctivitis sicca (KCS) before and after treatment with isotonic and one-half isotonic saline to compare treatment with these two solutions and to ascertain whether tear film osmolarity could be correlated with ocular surface disease. When 20 KCS eyes were treated with isotonic saline drops every three hours for one week, the average (+/-SD) tear osmolarity decreased from 365 +/- 77 mOsm/L to 329 +/- 47 mOsm/L, and the average (+/-SD) Rose Bengal staining score decreased from 4.1 +/- 3.1 to 3.6 +/- 3.3. There was no objective difference between treatment with isotonic and one-half isotonic solutions, in a double-masked comparison, however, four of five patients with diagnostically significant Rose Bengal staining preferred the half isotonic solution. There was a significant positive correlation between tear film osmolarity and Rose Bengal staining.