Retail and hospital pharmacies have separate rooms for manufacturing compounded medications. These rooms are equipped with, among other things, laminar flow cabinets. This enables a sterile manufacturing of eye medications, antibiotics medications, injection liquids and other drugs which have high requirements of microbiological purity. Maintaining a perfect cleanliness in rooms is a basis for conducting work in sterile conditions. Usable space and equipment should be properly cleaned and disinfected. Environmental purity tests were conducted in 20 pharmacies located in the province of Wielkopolska. Assessing the findings in accordance with purity class 4 it was found that the microbiological purity of air in four pharmacies did not meet adequate limits for this purity class. The investigation showed that laminar flow cabinets in two pharmacies had not worked properly. In moist environments, non-fermentable gram-negative bacilli were isolated. Patients who are administered compounded medications have reduced immunity, and what is more, metabolites produced by microorganisms may inactivate a medication. Preparing a microbiologically pure medication is, therefore, of paramount importance. Regular controls of microbiological purity of working environment in pharmacies thus seem justified.