Flow cytometric analysis of cell cycle progression in HUVEC cells treated with or without IFN-α (500 units/ml) and/or 5-FU (0.5 μg/ml). To synchronize the cell cycle in G0-G1, HUVEC cells were first pre-treated with 2 μM aphidicolin for 16 h. Cells were collected 12, 24, 48 and 72 h later. After pre-treatment by aphidicolin, the majority of cells (86.3%) were in G0-G1. At 24 h, IFN-α alone and IFN/5-FU increased the number of cells with S-phase DNA content. At 48 h and 72 h, IFN/5-FU still resulted in S-phase accumulation.