At 55 sites of a health institution in July and September 1990 a total of 161 specimens of arthropods were detected, 30 outdoors and 131 on the premises of the health institution. On their bodies 116 bacterial strains were isolated, mostly Gram-negative rods (more than 85%), in particular spp. Enterobacter, Acinetobacter, Klebsiella, Citrobacter and Pseudomonas. Gram-positive cocci accounted for cca 12%, in particular strains of S. haemolyticus and S. hominis. The greatest number of strains was detected on bodies of cockroaches, flies, Chironomus and Tenebrio. In about one third of strains the diffuse disk test revealed resistance to more than three antibiotics. The investigation was supplemented by microbiological examination of strains from a hospital environment (45 smears) and strains from biological material (82 specimens), from patients with nosocomial infections.