Recently, interphase cytogenetics using fluorescent in situ hybridization (FISH) was performed on various kinds of solid tumor, and their inherent karyotypic heterogeneities were revealed. Concerning this heterogeneity, we evaluated both the exhibiting number of chromosome 17 and nuclear DNA content on an identical nucleus by means of computer-controlled auto-scanning stage in order to demonstrate the alteration in number of chromosome 17 among cytofluorometrically distinct subpopulations.We investigated 8 lesions of surgically resected colorectal carcinomas, which were classified as aneuploid in quantitative DNA analysis and also exhibited an increase of 17-aneusomy nuclei. We used paraffin-embedded archival blocks. First, we prepared isolated cell specimens, and memorized the position of the cells on a glass slide using computer-controlled auto-scanning stage. Next, the specimens were stained with propidium iodide, and the fluorescent intensity was evaluated as nuclear DNA content in the order of cell position data. And lastly, FISH was performed with (peri) centromerespecific DNA probes for chromosome 17, and we enumerated the number of signals in a nucleus also according to cell position data. Then, we compared the distribution of number of chromosome 17 among cytofluorometrically distinct subpopulations. Three of 8 lesions showed a single GO+G1 peak, and the rest exhibited plural GO+G1 peaks in DNA profile. And 4 of 5 lesions, which showed plural GO+G1 peaks, presented a peak at the DNA value of (near) 2c. We could detect an alteration in the distribution of number of chromosome 17 between diploid peak and aneuploid peaks in 4 of 4 lesions which presented a peak at the DNA value of (near) 2c. However, we could ot find a difference in the distribution of number of chromosome 17 between GO+G1 peak and G2+M peak. These observations indicate that the distribution of number of chromosome 17 reflects an endoreduplication of genome content, yet, it does not alter in accordance with the phase of cell cycle. It is necessary to evaluate nuclear DNA content simultaneously in order to assess an essential cytogenetic change.