Four adenoid cystic carcinomas of salivary gland were studied by immunohistochemistry and immunoelectron microscopy with anti-actin, myosin, S-100 protein and GFAP antibodies. The results showed that neoplastic myoepithelial cells in these tumors gave positive reactions for actin, myosin and S-100 protein antibodies and negative reactions for GFAP antibody. The neoplastic myoepithelial cells lined the cyst-like spaces and surrounded the periphery of the epithelial nests. Neoplastic ductal epithelial cells were negative for the above mentioned antibodies. The differentiation tendencies and immunofeatures of neoplastic myoepithelial cells were discussed.