Medications used in 'Dry Eye' patients are reviewed for their effects on the corneal surface including the overlying tear film. Preservatives are discussed, since they affect the properties of commercial preparations which may be instilled frequently as a substitute for normal tears. The major beneficial effect which a topically applied agent can have on epithelium is to supplement or stabilise the tear film. Thimerosal sometimes triggers a sensitivity reaction, and other mercurial compounds are unstable. Benzalkonium chloride compromises both corneal epithelium and tear film. Some cationic detergents, including chlorhexidine digluconate and polyquat, cause less disruption at prophylactic concentrations. The use of a small drop size is helpful in preventing toxic effects of preservatives. All preservatives should be avoided when unit doses of a sterile tear replacement, such as saline, can be made available. Topical antibiotics should be used only to control known bacterial infections, avoiding high concentrations of bacitracin, gentamicin, and neomycin. Steroids and antibiotic/steroid combinations must be used with great caution, and only when uncontrolled ocular inflammation justifies the risk of possible corneal ulceration.