Three cases of monophasic glycogen-rich clear cell tumors of palatal gland origin were examined immunohistochemically and ultrastructurally in attempts to characterize their cellular composition. Despite their histologic resemblances, the clear cells from each case showed different immunohistochemical features. In case 1 the extensive positivity for vimentin and S-100 protein, in addition to the focal expression of actin and glial fibrillary acidic protein, strongly suggested that the clear cells were myoepithelial in nature. In contrast, the clear cells from case 2 exhibited both keratin and epithelial membrane antigen positivity, as well as ultrastructural features that suggested that they were glandular epithelial in nature. In case 3 no special markers except for keratin could be detected, indicating the less differentiated nature of the clear cells. These results show the heterogeneity of the clear cell tumor group of minor salivary glands.