How do bacteria find distant sources of food, and avoid noxious and potentially damaging environments? We seek answers to these questions by developing computer simulations of swimming bacteria exposed to gradients of different substances. Our programs include the molecular details of the intracellular signalling events allowing us to provide an integrated account of this simple behaviour at multiple levels. In this way, we have been able to uncover gaps in the present understanding of the phenomena and successfully predict novel mechanisms of intracellular signalling. We are also using our simulated bacteria as surrogate ?organisms? to test responses to defined gradients of attractants under conditions that would be difficult to achieve experimentally.