cell proliferation in emt6 tumours treated with single doses of xrays or hydroxyurea ii computer simulations a computer simulation technique was used to analyse data on the proliferation of clonogenic cells in emt6 tumours treated with 5 mgmouse of hydroxyurea hu or 30 gy 300 rads xrays this simulation technique is able to determine the respective roles of selective killing blocks in cell progression and recruitment of the treated population when the technique was applied to tumours treated with hu it was possible to prove that both a g1s block and recruitment occurred these phenomena could not have been demonstrated quantitatively or even qualitatively without the use of the simulation after irradiation blocks in cell progression and differences in the proliferative patterns of the surviving clonogenic cells and the total tumour cell population were found