Suspensions of flocculated aggregates subjected to flow present two distinct typical fragmentation mechanisms: cleavage and erosion. In this paper, a mathematical model is developed to concurrently evaluate the two phenomena. Erosion is tackled by a perturbative calculation, while cleavage is treated according to an exact calculation. The model is implemented on experimental data on the fragment size distribution in suspension of protein aggregates subjected to flow. Both cleavage and erosion are seen to gradually rise in significance as the flow rate increases. Their respective extent are each quantified with one chosen single parameter: cleavage with the number of fragments and erosion with the amount of eroded material. A relation found between the two parameters indicates a proportionality between the amount of eroded material and the surface area newly exposed by the process of cleavage. (c) 2007 Elsevier Ltd. All rights reserved.