The effect upon the tear film of a new tear substitute, Dacriosol, was compared to a non-viscous solution, saline, an to a highly viscous solution, Isopto Plain, in 15 normal healthy subjects and in 15 patients with mild to moderate keratoconjunctivitis sicca. No differences between the test solutions could be measured 3 h after last medication regarding: Schirmer's test, break-up time, rose bengal staining, corneal sensitivity and tear content of lysozyme. The test persons could not discriminate subjectively between the effect of the test solutions. The investigation parameters show an equal effect of Dacriosol, Isopto Plain and saline both in normal healthy subjects and in patients with keratoconjunctivitis sicca.