The principle of cytological profiling. Cells are treated with test compounds at varying concentrations and then stained with reagents that detect various cellular proteins or organelles. In this example, cells are treated with reagents that detect cellular DNA, the Golgi apparatus, or microtubules. Compound 1 shows a profile characteristic of a microtubule stabilizer, which leads to longer microtubules but dispersed DNA and Golgi apparatus as a result of the mitotic arrest that is a secondary consequence of microtubule stabilization. Compound 2 has more subtle effects, inducing changes in nuclear size and shape, with little effect on microtubules and only a small shift in the position of the Golgi. In an actual experiment (such as in ), cytological changes are measured at a variety of different drug concentrations, and a variety of measurements are made on each image. This complex dataset is then reduced using various statistical approaches to identify the key parameters that change as a function of drug concentration.