AbstractWe have applied DNA flow cytometric analysis to paraffin‐embedded tissue sections of primary malignant melanomas. Conventionally, flow cytometric analysis of paraffin‐embedded tissue sections has been done by the method of Hedley et al. We added ultrasound treatment to the method of Hedley et al. and a lower value of coefficient of variation was shown. Furthermore, a new technique, fluorescencein situhybridization with a chromosome‐specific repetitive DNA probe, was used for the analysis of chromosomal numerical aberrations in the same paraffin‐embedded tissue sections. The DNA flow cytometric analysis showed that in 8 cases six primary malignant melanomas were of the aneuploid pattern and two cases of lentigo maligna (melamonain situ) were of the diploid pattern. By fluorescencein situhybridization, the two cases with the diploid pattern had spots/nucleus of 1.28 and 1.12, and those with the aneuploid pattern had spots/nucleus from 2.01 to 2.27. Only one nodular melanoma in an aneuploid case showed spots/nucleus of 1.71. These data indicate that fluorescencein situhybridization with chromosome‐specific repetitive DNA probes can serve as a cytogenetic tool for the analysis of interphase nuclei of solid human tumors and may be useful for the study of tumor cell hete