Clonogenic activity of various hematopoietic progenitors and stromal cells in bone marrows of p53+/+ (black bars) and p53−/− (shadowed bars) mice analyzed on days 0, 2, 4, and 6 after 5-FU treatment. Results are mean (standard deviation) from three independent experiments. Y axis, number of colonies; X axis, days after 5-FU treatment.