Nuclear DNA contents were comparatively determined by flow cytometry in primary and metastatic lesions from 112 cases with stomach cancer. Aneuploidy frequency and mean DNA index were higher in lymph node metastatic lesions than in primary lesions, both resected synchronously. In these lymph node metastatic lesions, DNA ploidy patterns did not change in 79% (89/112 cases), and did change in 21% (23/112 cases). Concordance of the DNA index between primary lesions and synchronous liver metastatic lesions was seen in 63% (5/8 cases), but the concordance rate was only 25% (4/16 cases) for primary lesions and metachronous liver metastatic lesions and 0% (0/8) for primary lesions and lung metastases. DNA ploidy changes in metastatic lesions were marked in distal metastatic lesions, or more marked in metachronous metastases than in synchronous ones. The results of the present study suggested the possibility of detecting changes in biological characteristics of metastatic lesions by flow cytometric DNA analysis.