Prolactin has been reported to be present in the tear film of humans and prolactin-like immunoreactivity has been detected by immunofluorescence in acinar cells of the lacrimal glands of humans and rats. The present study was aimed at clarifying the intracellular distribution of the prolactin-like immunoreactivity, using the electron microscope immunogold technique. The lacrimal gland acinar cells have two types of secretory granules: 1) Secretory granules containing flocculent materials irregularly shaped and are often coalesced. 2) Secretory granules are fairly round and contain homogenous materials of a moderate electron density. The density of the granular content varies even within a single cell. We found prolactin-like reactivity in secretory granules, some smaller cytosolic vesicles, Golgi cisternae and nuclei in acinar cells from intact glands of rat. Our present results are consistent with the conclusion that prolactin is present in lacrimal cells. The presence of prolactin reactivity in the nucleus suggests that prolactin may be a regulatory factor modulating gene expression.