Electron microscopic immunocytochemistry was used to investigate the distribution of four secretory proteins within the granules of human parotid and submandibular gland acinar cells. The results demonstrate that the distribution of the individual proteins differs significantly. Amylase is concentrated within the electron-dense regions of the granules, whereas agglutinin is present mainly in the regions of lower density. In contrast, the proline-rich proteins and histatins are distributed throughout the content of the granules and do not appear to be concentrated in either the high- or low-density regions. The results also suggest that different mechanisms, such as self-aggregation or ionic complexes with metal ions and charged macromolecules, may be involved in the packaging of individual proteins within the same granule. Further, they also show that among the salivary glands of various species, the intragranular distribution of similar proteins (e.g., amylase and proline-rich proteins) may differ.