In the present investigation we have examined the presence, distribution and probable role of acid phosphatase in lenses of normal and galactose-fed rats. Acid phosphatase was localized in lenses using two separate cytochemical procedures (Gomori and Barka Anderson methods) and examined at the ultrastructural level. Both procedures, in general, provided similar sites of acid phosphatase activity, although with the Barka-Anderson method finer and larger amounts of well-defined reaction product were observable at the site of reaction. The reaction product was observed in lenses of both rats fed on regular laboratory chow and galactose-fed rats. The intracellular location of the reaction of this enzyme was primarily in lysosomes and occasionally in the endoplasmic reticulum cisternae. At the extracellular sites, it was near the epithelial cell membranes which abut each other and cortical fibers. However, in the cortical fibers the extracellular localization was at various sites on the entire intercellular space between neighboring fibers. The possible role of hydrolases in the lens tissue is discussed.