The association with time (0–60 min) of an eye drop preparation containing sodium hyaluronate with the corneal epithelial cell surface was examined using both cryo-fixation and osmium tetroxide vapor fixation and scanning (SEM) and transmission electron microscopy (TEM). In phosphate-buffered saline (PBS)-treated control eyes of adult mice, 37 postnatal days (PND) old, a variably thick, but well-defined preocular mucus coat was seen, while 5-PND-old animals treated with PBS lacked morphologically detectable mucus at the corneal surface. In mice of both ages, the eye drop preparation was detectable at the corneal surface at time 0 and 5, 15, 30 and 60 min after its application. For these time periods, in both the adult and the pup, the eye drop preparation containing sodium hyaluronate appeared to be composed of electron-dense filamentous material (TEM) which associated with corneal surface cell microvilli. SEM revealed that the eye drop preparation was globular in composition and that its distribution became patchy over the cornea with time for both the adult and the pup.