In this work, the magnetorheological properties of suspensions of micron-sized iron particlesdispersed in magnetite ferrofluids were studied. With this aim, the flow properties ofthe suspensions in the steady-state regime were investigated using a commercialmagnetorheometer with a parallel-plate measuring cell. The effect of both magnetite andiron concentration on the magnitude of the yield stress was studied for a broad range ofmagnetic fields. In addition, the experimental values of the yield stress were compared withthe predictions from the chain model. With this purpose the values of the yield stresswere obtained by means of finite element calculations. Interestingly, it was foundthat the experimental yield stress increases with the concentration of magnetitenanoparticles in the ferrofluid. Unfortunately, this behaviour is not obtained fromcalculations based on the chain model, which predict just the opposite trend.