In this paper, we measured the local initial deposition rates of streptococci to adhering actinomyces, acting as protruding local sinks on a glass collector, as a function of the actinomyces density in a parallel plate flow chamber. The local initial deposition rates, i.e., deposition in the vicinity of actinomyces, j(0,1) compared well with values predicted by a model based on convective diffusion perpendicular to the collector surface and convection parallel to the collector surface when the seeding density of adhering actinomyces was below 0.5 x 10(6) cm(-2) (0.03% surface coverage). However, at higher sink densities the model breaks down due to particle depletion of the suspension downstream of a protruding sink.