Transport of water-soluble substances between the peritoneal cavity and the plasma was modeled with a distributed approach. The model includes diffusion and convection through tissue as well as membrane transport across blood capillaries, which are assumed to be distributed uniformly in the tissue. Lymphatic uptake via the diaphragm is also included. Transport in the remainder of the body is modeled by a system of compartments. The resulting system of mass balances and rate equations is solved numerically to provide predictions of peritoneal volume and concentrations in plasma, peritoneal fluid, and tissue surrounding the cavity. The model sensitivity is explored by varying key parameters to determine whether the changes would have a significant effect on model output. Key parameters include peritoneal surface area, tissue diffusivity, capillary permeability, tissue void fraction, and hydrostatic and osmotic pressures in the capillaries and interstitium.