On-line process analysis requires material to be passed through a sampling line to an analyser for measurement. With batch processes, this is often achieved using a fast sampling loop. In this work, a review of sampling systems for stirred vessels is presented. The aim is to outline the main aspects to consider when selecting and designing an effective sampling device for a stirred tank reactor. The importance of factors such as probe location, orientation of the probe and sampling velocity is highlighted. The main conclusion is that the sample probe should be positioned horizontally at the stirrer plane, between the stirrer blade and the reactor wall, in order to achieve optimized sampling from heterogeneous systems. It is also preferable to use a pump able to provide a flow rate at least equal to that required for isokinetic sampling conditions in the fast loop.