Eighty-four intubated, mechanically ventilated patients were prospectively evaluated for incidences of colonization and nosocomial pneumonias dependent on whether they received endotracheal suctioning by an "open" suction method vs. "closed" suction (Trach Care Closed Suction System) method. Results show that closed suctioning is associated with a significant (67% vs. 39% p less than .02) increase in colonization compared with open suctioning. However, difference in the incidence of nosocomial pneumonia was not significantly (26% vs. 29%) different between closed and open suctioning. Differences in severity of illness (Acute Physiology and Chronic Health Evaluation II and Therapeutic Intervention Scoring System), age, sex, presence of NG tubes, use of H2 antagonists or antacids, use of antibiotics, and history of smoking were all nonsignificant. Survival analysis demonstrated that the probability of survival without developing nosocomial pneumonia was greater among closed-suctioning patients vs. open-suctioned patients (p less than .03). This study shows that suctioning performed via the Trach Care closed-suction system increases the incidence of colonization but not the incidence of nosocomial pneumonia, and may actually decrease mortality when compared with open-suction systems.