Transforming growth factor (TGF)-β1 induced a robust decrease in S-phase in non-cancer cell strains. Human primary cells and human and mouse established cell lines were treated with (TGF-β1) or without (control) 5 ng/ml TGF-β1 for 48 hours. The cells were then harvested and incubated with propidium iodide, and DNA content was determined using a FACS Caliber (Becton-Dickinson). Data were modeled and analyzed using ModFit and WinList software (Verity Software House). Fifteen thousand events were analyzed for each sample. Representative histograms are presented illustrating cells that had a robust decrease in S-phase (NMuMG), modest decrease in S-phase (EpH4), and no decrease in S-phase (MDA-MB-436) as a result of TGF-β1 treatment. G0/G1 and G2 phases are indicated by black shading and S phase is indicated by gray shading on the histograms. The percentage of cells in G0/G1 and in S phases of the cell cycle are indicated. Three independent experiments were performed with three replicates per experiment.