This study presents the results of an automatic classification of six purely papillary, five purely follicular and five mixed papillary-follicular carcinomas of the thyroid. All cases were correctly classified with only two chromatin textural parameters obtained in the Olga's scan software package developed in our laboratory. Chromatin texture lines were generated by a unidirectional grey level gradient, obtained as a natural logarithmic function of the integrated optical density of each nucleus; this increased the difference between clear papillary and granular follicular nuclei. The accuracy of the method allowed a follicular carcinoma to be correctly classified as a mixed follicular-papillary. Finally a columnar-cell carcinoma of the thyroid was detected by means of its atypical DNA histogram.