A complex fluid submitted to strong flows can endure irreversible changes in its structure. This is the case for long chain polymer additives that are commonly used as viscosity enhancers in industry, notably for oil recovery. These polymers break in solution when submitted to high deformation rates, eventually causing a serious viscosity loss. This problem of practical importance is though difficult to handle from a fundamental point of view given its complexity. We introduce here a new tool, based on microfluidic technology, for the screening of the degradation of solutions in the model situation of the flow through a constriction. We integrate two functions in a single set-up, a micro-fabricated constriction and an on-chip viscosimeter. This tool enables us to probe rapidly the viscosity loss imparted by flowing through the constriction at a given flow rate. Thanks to microfluidics, the sample preparation and measurement time are significantly lower than those implied by classical measurement protocols (reduction by up to two orders of magnitude). In addition, confinement provides control of the flow in terms of inertia. To illustrate the potential of this approach in a screening perspective, we use this tool to study the degradation of a series of semi-dilute aqueous solutions of PEO of varying molecular weights and concentrations. For each solution we identify a threshold flow rate for polymer degradation. The corresponding critical deformation rate decreases with molecular weight and concentration, as expected (the mass dependence is in line with previous reports and theories for dilute solutions). In addition we characterize the viscosity loss for larger deformation rates and find that, despite the polydispersity of our solutions, the observations for the various solutions can be roughly recast on a master curve by renormalization of the imposed deformation rates according to a law M(W)(-1.7 +/-03)c(-0.7 +/- 03). (C) 2010 Elsevier B.V. All rights reserved.