Measurements were taken of the bulk rheological properties of concentrated suspensions of particulates in unsaturated polyester resins using a cone‐and‐plate rheometer. Over the range of shear rates investigated, suspensions of calcium carbonate showed Newtonian behavior, whereas suspensions of clay showed both yield behavior at low shear rates and shear‐thinning behavior at high shear rates. Suspensions of both calcium carbonate and clay together exhibited no normal stress effects. However, suspensions of polyethylene powders were found to exhibit positive values of normal stress at low concentrations, but negative values of normal stress at and above a certain critical concentration. In view of the fact that negative values of normal stress were observed at low shear rates(1–10 s−1),the possibility of inertial effects is ruled out because we observed inertia‐induced negative values of normal stress with three different Newtonian liquids at very high shear rates, say above250 s−1.Having checked the possibilities of other probable sources that might have caused the negative normal stresses observed, we have concluded that the negative values of normal stress observed with concentrated suspensions of polyethylene powders in unsaturated polyester resin are real, not an artifact. Interestingly enough, the normal stress effects observed with concentrated suspensions of polyethylene powders very much resemble the observation reported by Kiss and Porter, who used liquid crystalline polymer solutions.