Intermittent mandatory ventilation (IMV) was introduced to facilitate the weaning of patients from mechanical ventilation. The outcome of ventilator management in 116 patients who were treated in the first 3 mo. of 1975 was compared retrospectively with that of 135 patients who were treated in the first 3 mo. of 1976. All patients who were treated in 1975 received conventional (assisted or controlled) mechanical ventilation. In 1976, 77 patients (57%) were treated with the use of IMV and 58 (43%) with conventional mechanical ventilation. Sixty-five patients who were treated in 1976 with the use of IMV were matched with patients who were treated in 1975 with conventional ventilation, on the basis of age, sex, race, history of pulmonary disease, smoking history, diagnosis, service and location of therapy. The average time spent on a ventilator by the IMV patients was 145 vs. 142 h for the matched control patients. The length of hospitalization was 36 days for the IMV patients and 30 days for the control patients. These time periods were not significantly different and indicate that IMV did not reduce the length of ventilator management.