Class C cleanrooms require the largest areas in the aseptic production of pharmaceuticals and therefore also the largest air volumes to maintain air purity. The FDA Aseptic Guide describes an air change rate of 20/h as "typically acceptable". The extent to which this value is necessary to comply with the limit values for particles and colony-forming units (CFU) in accordance with the FDA guidelines and EU GMP Annex 1 was investigated in an experimental study. It was shown that when suitable cleanroom clothing is used, a 10-fold air change is sufficient to reliably comply with the specifications for both particles and the permissible germ load.