The in-line rheometer concept based on the combination of the ultrasonic velocity profiling (UVP) technique and pressure difference (PD) measurements was utilized for investigating the influence of particle concentration and size distribution on the rheology of particulate suspensions in pipe flow under realistic industrial process conditions. Well defined model suspensions were used, consisting of 11mm and 90mm diameter polyamide particles suspended in rapeseed oil at concentrations ranging from 1 to 25% by volume. The variation of concentration and particle size distribution had the expected effects on the shear viscositiy of the investigated unimodal and bimodal suspensions. The in-line results showed that the investigated suspensions exhibit Sisko flow behavior and demonstrated that the UVP+PD method can be used to determine the flow behavior of complex fluids and suspensions, even at high solid concentrations, under industrial conditions in-line. The obtained inline results were in good agreement with measurement data obtained using a conventional rotational controlled-stress rheometer. Limitations of commercially available transducer technology were identified and other possible sources of inaccuracy of the UVP+PD method were investigated. Several improvements of the UVP+PD measurement method were proposed.