Three hundred forty-five children under 16 years of age with pneumonia confirmed by roentgenogram were studied to determine in what way the leukocyte count correlates with the patient's clinical course. The study confirms that the initial white blood cell count indeed helps predict which child will respond rapidly to antibiotic therapy. Several other factors correlate as well: those with lobar pneumonia and those with higher fevers are more likely to respond promptly. However, the total white blood cell count provides additional predictive information within each of these categories as well. The number of band forms did not correlate with clinical response nor with any other of the indices measured. The presence of pneumococcus in the nasopharynx also had no predictive value. The differential white blood cell count added minimal additional information, but only when the total count was below 15,000/cu mm.