To determine observer agreement for a clinical score and oximetry in lower respiratory infection in children less than 2 yr of age, a convenience sample of 56 infants hospitalized with bronchiolitis or pneumonia was assessed independently by two observers. A total of 12 infants had chronic lung disease of prematurity or congenital heart disease. Infants in whom oxygen supplementation could not be discontinued for at least 5 min were excluded. A severity score was assigned for each of four categories (respiratory rate, retractions, wheeze, and general appearance). A total for each patient was obtained by summing the score for each category. Oxygen saturation was measured using a Nellcor oximeter. Agreement beyond chance was measured using the kappa statistic. The relationship between observers for total score and oximetry and the mean total score and mean oximetry value for each patient was expressed as a Pearson correlation coefficient. A total of 56 infants and children were studied: 2 had pneumonia, 11 had an exacerbation of pulmonary signs and symptoms with their underlying cardiac or pulmonary disease, and 43 had bronchiolitis. Kappa was 0.48 for general assessment, 0.38 for respiratory rate, 0.31 for wheeze, and 0.25 for retractions. All values were statistically significantly greater than 0 at p less than 0.01. Correlations for total score and for oximetry were 0.68 and 0.88, respectively. The median difference between oximetry readings was 1. The correlation coefficient between total score and oximetry was -0.04. The limited agreement for clinical signs makes comparison of patient illness severity between studies difficult.(ABSTRACT TRUNCATED AT 250 WORDS)