The rheological behaviour of highly filled polymer systems used in powder injection moulding (PIM) technology influences strongly the final properties of the products. The study of the influence of particle size distribution on the rheological properties of 316 L stainless steel feedstocks is presented. Two kinds of gas-atomized powders were employed with d(90) of 8 and 26 mu m of particle size. Five feedstocks were prepared at powder loadings of 50, 55, 60 and 65 vol.%. employing both starting powders and their own mixtures in volume ratios 25/75. 50/50 and 75/25. The binder was composed by 50 vol.% of high density polyethylene and 50 vol.% of paraffin wax. Feedstocks were prepared in a torque rheometer with a pair of roller rotor blades and rheological measurements were performed in a capillary rheometer. The effects of the powder loading and different particle size distributions on the rheological properties of feedstocks were investigated. Different rheological parameters, like melt viscosity, power flow index and activation energy were determined. A relationship between powder characteristics and rheological behaviour was established. (C) 2010 Elsevier B.V. All rights reserved.