M.Cur. / The South African Nursing Act (Act 50 of 1978) views the professional nurse as an independent practitioner, her independent function being the right to make decisions and taking the full responsibility for such liability. The professional nurse's liability depends on her authority, skills and responsibilities. Her role in the intensive care unit is aimed at optimal care of the ventilated patient, thus providing physical, psychological and spiritual well-being. The incidence of micro-organism colonization in the lower airway of the ventilated patient is researched in this study and nursing guide-lines are set out for the correct use of the ventilator. A contextual, descriptive study was carried out to: (a) determine the sterility of the humidifier reservoir and ventilator tubes; (b) determine which micro-organisms are present in the lower airways of patients after they have been ventilated; (c) set out guide-lines for the nursing staff on how to correctly use the ventilator. Sample analysis was done from the following: The sterile water in the reservoir prior to ventilation. Sputum obtained prior to extubation. Water from the reservoir after extubation (waterbasin of the humidifier). The water present in the ventilator tubes after extubation. The following conclusions were made: contamination is caused by the nursing staff; there was no migration of micro-organisms from the water reservoir to the circuit; the organisms in the ventilator circuit differed from those found in the lower airways of the patient...