The Tissue and Cell Bank (TCB) at the Department of Transfusion and Regenerative Medicine of the Sestre milosrdnice University Hospital Center is an organized clinical unit in which the activities of collecting, taking, processing, preserving, storing and distributing human tissues and cells intended for clinical use are performed. Within TCB, a Tissue Engineering Laboratory was built in accordance with Good Manufacturing Practice (GMP) and clean room technology. In a laboratory working with cells / tissues of human origin, it is crucial to control the level of cleanliness of air, contact surfaces, laboratory equipment, staff clothing, water from critical laboratory equipment as well as nutrient cell medium, aliquots and tissue grafts. The aim is to determine the type and number of colonies of the most common microorganisms by continuous sampling and to determine their importance for the safety of the entire process of aseptic tissue and cell production. Laboratory workers are the main source of contamination, which is confirmed by the fact that in all classes of clean space, the most common bacteria are Staphylococcus (coagulase-negative staphylococcus, CoNS), Micrococcus and Bacillus. Microbiological analysis of samples is performed at the Department of Microbiology at the Croatian Institute of Transfusion Medicine with the aim of detecting the presence of aerobic and anaerobic bacteria and yeasts and molds. The permitted number of colonies for clean rooms is defined according to the GMP standard and must not be exceeded.