Secretions from the meibomian gland are believed to be important in reducing ocular surface water evaporation and preventing dry eye. Patients with blepharitis frequently have meibomian gland dysfunction with loss of meibomian glands (drop out). The authors hypothesized that dry eye that often occurs in patients with chronic blepharitis is secondary to increased evaporation associated with gland loss. The authors measured the ocular surface water evaporation and tear osmolarity of patients with meibomian gland drop out and patients with gland drop out with a low Schirmer test. These findings were compared with those of a control group. The authors found that eyes with meibomian gland drop out and those with drop out and a low Schirmer test had a significantly higher evaporative rate at 30% relative humidity (average, 49.9 +/- 21 x 10(-7) g/cm2/second, or 0.49 +/- 0.29 microliters/minute evaporative loss per eye, and 59.1 +/- 28 x 10(-7) g/cm2/second, or 0.58 +/- 0.23 microliters/minute, respectively) when compared with those in the control group (average, 14.8 +/- 6 x 10(-7) g/cm2/second, or 0.15 +/- 0.07 microliters/minute [P < 0.05]). There was a significant correlation between evaporative rate and gland drop out (r = 0.522). Patients with meibomian gland drop out, and especially those with low tear production by Schirmer test, have an increased risk of dry eye developing through increased evaporation.