The development of pneumonia was monitored in head-trauma patients requiring mechanical ventilation. Of the 66 patients studied, 15 (23%) developed pneumonia within 14 days after ICU admission. In each case the diagnosis was based on x-ray evidence and at least two of the following: increased white blood cell count, increased fever, and/or increased sputum production with a predominant organism on the sputum stain. Coagulase-positive Staphylococcus aureus was the most common etiologic agent. There was no difference in the occurrence of pneumonia between patients treated with no steroids or with low, moderate, or high steroid doses. Although there was an association between thiopental use and the development of pneumonia, dexamethasone treatment was not a significant risk factor in the development of pneumonia in this patient population.