Thirteen lymph node biopsy specimens with Hodgkin's disease (six cases of the nodular sclerosis type; six cases of the mixed cellularity type; one case of the lymphocytic depletion type) were studied with scanning cytophotometric measurements. The DNA content of small lymphocytes, large lymphocytes, atypical mononuclear cells and Hodgkin cells was measured. The sizes of the nuclei and mitotic indices were also measured. There were no lymphocytes with aneuploid DNA stemlines. Large lymphocytes showed proliferative activity which is possibly reactive, although its neoplastic character cannot be excluded. Hodgkin cells exhibited aneuploid values in seven cases and atypical mononuclear cells in only four cases. The nuclear sizes and the DNA content of the atypical mononuclear cells ranged between the values of lymphocytes and Hodgkin cells. The mixed cellularity type showed higher DNA values, more frequently occurrence of aneuploid stemlines and a higher frequency of mitotic figures than did the nodular sclerosis type. The results confirm the different grades of malignancy of the various histopathological categories of Hodgkin's disease.