The simplest method is cell count through staining and visualize under microscope using hemocytometer.  

...or to look at their behavior at a flow cytometer: FSC-A vs. SSC-A

Both Ahmed and Jochen have great suggestions. A third question for you, Sarjan, is what techniques do you have available to you? Fluorescence microscopes? Flow cytometers? Etc.

Hi,

Using cell counting with trypan blue, MTT, XTT ......