In conjunction with nosocomial infection of opthalomycoses in the ophthalmological department, from the enucleated eye and from Ringer solution (used during operations) a fibrous microscopic fungus Paecilomyces lilacinus was isolated. During sensitivity tests of the isolated strain to locally used disinfectants and chemical sterilizing agents it was revealed that the strain was not killed even by the action of higher concentrations of disinfectant solutions, used in our health departments according to instructions of the Ministry of Health of the Slovak Republic. Persteril, although supposed to act as a chemical sterilizing agent 0.5% concentrations and 10 minute exposure, killed the isolated strains only in the course of 30 minutes. Based on tests of the strain Paecilomyces lilacinus it must be foreseen that in health institutions strains of microorganisms may be present which are resistant to these concentrations of disinfectants which are considered effective.