DNA flow cytometry was used to quantitate changes in distribution of cells in each phase of the cell cycle during postnatal development of the mouse pancreas. From birth through day 20 the cells in each phase remained relatively constant, after which there occurred increases in G₂-M and S phase cells and a decrease in G₀-G₁ phase cells. Polyploidy first became evident at 20 days and increased to 9% by the adult stage at 90 days. The importance of polyploidy is discussed as it may represent a parameter that can be exploited to detect and evaluate the progression of changes in the pancreas of diabetics.