Measurement of Chemotaxis.

http://en.wikipedia.org/wiki/Chemotaxis

A wide range of techniques is available to evaluate chemotactic activity of cells or the chemoattractant and chemorepellent character of ligands. The basic requirements of the measurement are as follows:

• concentration gradients can develop relatively quickly and persist for a long time in the system
• chemotactic and chemokinetic activities are distinguished
• migration of cells is free toward and away on the axis of the concentration gradient
• detected responses are the results of active migration of cells