In most organisms, cells exit the cell cycle at G1 and enter G0 during terminal differentiation. But for Dictyostelium, the accepted, albeit controversial, model is that cells differentiate into spores or stalk cells from G2 in response to starvation. Chen et al. now propose that tissue-specific regulation of arrest occurs before terminal differentiation in G1 in this organism (see p. 2619). Their flow cytometry analyses of cellular DNA content and their measurements of chromosome copy number and chromosomal DNA synthesis during development indicate that all the cells pause in G2 at the onset of development before undergoing one cell division. Prespore cells divide first,12-18 hours into development; prestalk cells divide later, up to 22 hours into development. After this division, both cell types arrest in G1. These important results provide the basis for understanding the key role that the cell cycle plays in cell-type specification in Dictyostelium.