In close cooperation with BAT Southampton, a smoking machine was developed, which generates cigarette smoke for in vitro research. The machine called RM20S is based on the rotary principle of the RM20H. It is able to smoke four different brands simultaniously under ISO conditions. The machine dilutes the smoke and forwards the dilution into the cell chambers. The fully automated process offers the possibility to supply the cell chambers with smoke for several hours. The general advantage of the rotating principle is that all necessary tools like loader, lighter and so on are only needed once. The cigarettes are subsequently moved to the respective position. The smoke ring offers four cigarette holders, which are moved into five positions: loader, lighter, smoke position, diluting, glow detection and extraction. The machine is equipped with four independent stepper motor driven syringes with an adapted 5/4-direction-control-valve for selecting the flowpath. The syringes and valves are designed such that residua does not effect the function. The hood and air flow control allowes to smoke under ISO 3308 conditions. The machine is controlled by several micro processor systems which operate to the master slave principle. For operation the machine is equipped with a terminal with display, keyboard and printer.