Nasal drops and nasal sprays are commonly supplied in multi-dose containers that usually include suitable levels of an appropriate preservative in order to kill or prevent growth of any microorganisms which might enter the dispensing system. Preservatives should both protect the patient from infection and prevent spoilage of the product. Unfortunately, preservatives often cause unwanted side effects; in particular, the nasal mucosa is irritated frequently. Consequently, the use of preservatives in nasal preparations should be avoided. The technical design of the 3K system, a new multi-dose container, combines several microbiological safety features and therefore allows use without preservatives. Earlier tests have shown its safety for 6 weeks after the first opening. In order to test the microbiological safety of this multi-dose system over longer time periods, an in-use stability test was designed. The results revealed that the first dose as well as the contents complied with the requirements of the European Pharmacopoeia. Therefore, from a microbiological point of view for the tested nasalia in the 3K system, the stability after opening could be extended from 6 weeks up to several months without loss of microbiological quality.