Bacterial chemotaxis of a marine Pseudomonas induced by transition metal ion concentration gradients has been demonstrated. It is shown that Cu(II) and titanium ions are strong chemo-attractants providing a long range recognition mechanism for the colonization of corroding surfaces of engineering materials, The effect of titanium ions is particularly unusual as strong chemotaxis has also been observed with aqueous solutions saturated with solid TiO2. A diffusional model using a variable bacterial diffusion coefficient has been employed to evaluate the movement of bacterial populations. The non-linear diffusional problem has been simulated using a simplified finite differences approach. A value of 1.5 x 10(-5) cm(2) s(-1) for the apparent bacterial diffusion coefficient (or random motility coefficient) has been calculated.