Experiments in cultured cells have shown that different cell lines can respond in different ways to the very same mitotic injury and that the response (apoptosis, mitotic catastrophe, stable mitotic arrest, mitotic slippage followed by growth arrest etc.) determines whether the cells die from or survive the treatment by an antimitotic agent. What is known about the response of cells to antimitotic drugs in vivo? To what extent is the type of the response determined by the cell and tissue type, tumor grade, or by other factors? Can the type of the response change in the course of cancer therapy and if so, can such a change have a prognostic value?