Fluid cell membranes are the main barrier to drug absorption when diffusion limits uptake. Immobilized artificial membranes (IAMs) are solid phase models of fluid membranes that predicted oral drug absorption in mice for a homologous set of cephalosporins. IAMs also predicted drug permeability through Caco-2 cells. Since drug permeability in Caco-2 cells is known to correlate with the oral absorption of drugs in humans, IAMs may also model drug absorption in humans. IAM analysis is experimentally simple, and large-volume screening of experimental compounds for drug absorption is possible.