A kinetic transport model with the ability to account for variations in cell density of the aqueous and solid phases was developed for bacteria in porous media. Sorption kinetics in the advective-dispersive-sorptive equation was described by assuming that adsorption was proportional to the aqueous cell density and the number of available sites on the solid phase, whereas desorption was proportional to the density of sorbed cells. A numerical solution to the model was tested against laboratory column data, and the performance was compared with that of a two-site model. The kinetic model described the column data as well as the two-site model did, but the highest efficiencies of both models were associated with experiments with the smallest sorption. Furthermore, the kinetic model accounted for cell density dependent sorption, as demonstrated by fair predictions of bacterial transport at one cell density when using parameters obtained at another cell density. ¿ American Geophysical Union 1994