An epidemiological study on the wide spreading of nosocomial infections among patients admitted to intensive care units in Bulgaria is carried out, covering the period 1982 through 1996. The proportion of nosocomial infections registered in the aforementioned wards accounts for 4.66 +/- 0.33 per cent of the overall in patient infectious pathology. Eight per cent of the patients discharged from intensive care units develop infections originating in hospitals. The predominant nosological entities recorded include pulmonary infections, operative wound suppurations and urinary system infections. More than 15 microorganisms, causing agents of infectious processes, are isolated with E. coli ranking first, followed by Staphylococcus spp., Pseudomonas aeruginosa, etc. The partial registration of nosocomial infection cases in the various intensive care units interferes greatly with the practical implementation of updated and adequate measures for prophylaxis and struggle against the infections. Thus, conditions are created promoting prolongation and rising cost of the inpatient treatment, continuous disability, premature death and reduced efficiency of the medical cares delivered.