When transferring a process from stainless bioreactors to disposable bioreactors there are many factors to consider, including, process robustness, culture reproducibility, oxygen transfer, heat transfer etc. The benefits in terms of eliminating CIP, SIP, reduced validation and WFI make the transfer most definitely worthwhile. The costs of disposables compared with conventional stainless-steel bioreactors are lower because the capital investment is lower. Therefore, the necessity for qualification and validation processes, as well as maintenance, is reduced. A new single use stirred tank bioreactor - the Biostat^® CultiBag STR will be introduced. Real time growth and productivity data comparing actual stainless steel to disposable will be shown. Additionally disposable sensors for pH and DO replace the traditional labor intensive polarographic and galvanic sensors. Single use sensors eliminate the need for risky and time consuming tasks such as sterilization, calibration and aseptic insertion into the bag.