The morphology of fouling layers is an important factor in modeling permeate flux behavior in membrane filtration. In the present paper, the relationship between the chemical composition of suspension and the morphological properties of the deposit formed from the suspension was studied. The deposition from binary sus pensions of particles with different collision efficiencies as a prototype for naturally occurring heterogeneous suspensions was simulated using the 2D on-lattice deposition model. Simulation results were qualitatively compared with transmission electron microscopy and energy-dispersive X-ray analysis of fouling layers produced in a series of pilot filtration experiments. For the case of deposition from binary suspensions, different degrees of segregation of chemically distinct particulate fractions in the fouling layer were observed. Similar deposition patterns were observed in the pilot filtration experiments; the fouling layers consisted of an organic matrix with dendritic inclusions of metallic nature. These findings prompt reevaluation of the model of resistances connected in series for the fouling layer resistance usually employed to describe permeate flow. Chemical heterogeneity of suspension may result in the formation of fouling layers with substructures of different specific resistances to permeate flow. The total resistance can be expected to be less than predicted in the assumption of a chemically homogeneous suspension.