Whether spermatocytic seminoma (SS) develops during meiosis or not is still controversial. To determine that, the DNA content of large, small, and intermediate cells of SS was measured by cytofluorometry to obtain DNA histograms for each cell type. The large cells were aneuploid and showed cell cycles with G0/G1 DNA values from 3C to 18C. The ploidy of the large cells doubled stepwise (i.e., 4.5C-9C-18C, 3C-6C-12C, and so forth). The small cells showed distinct cell cycles with a DNA content of 2C or near 2C, and the intermediate cells showed both diploid and aneuploid DNA values. It is speculated that none of the cell types is involved in meiosis, based on the fact that each size of cell appears to have its own cell division cycle. It is concluded that in SS, the diploid cell cycle formation by small cells and the creation of large cells by continuous sequential polyploidization result in the morphologic expression of three types of cells (large, small, intermediate).