Biofilm processes are of interest to researchers in a variety of fields including bioremediation, oil recovery, wastewater treatment, medicine, and dentistry. In this paper we describe how this complex, dynamic, fluid-structure interaction can be modeled successfully using the immersed boundary method. The model presented here includes the coupling of hydrodynamics; substrate reaction, diffusion, and convection; as well as the chemotactic response of swimming microbes. Cell-cell aggregation and cell-substratum adhesion are modeled by generating appropriate binding forces between discrete representations of organisms that may hold them together, or ii fluid stresses are large, may yield and release the organisms. In this paper, we show two-dimensional numerical simulations to demonstrate several different types of scenarios that may be modeled using immersed boundary methods. These simulations indicate the variety of different phenomena one might expect in biofilm processes. (C) 1996 Academic Press, Inc.