Single-cell DNA cytophotometry has been assessed on histological sections or aspiration biopsy smears from 13 parotid acinic cell carcinomas and has been related to prognosis. The minimal follow-up was 6 years. Six ACC were well differentiated and seven moderately well differentiated. The modal DNA values of all tumours examined were in the diploid area. The number of nuclei above 2.5C DNA, expressing proliferative ability or aneuploidy, was low. A difference, too small to be of value for prognostic purposes, was found between the non-recurrent tumours (6%) and the metastasizing tumours (16%). The DNA levels measured in the present tumour material correspond to the concept of ACC as being a well differentiated neoplasm. The nuclear DNA pattern of these tumours would seem to be of minor prognostic significance with regard to survival time and/or potential for metastasis.