The role of bronchoalveolar lavage (BAL) in children remains to be defined, and to date there has been no standardization of acquisition and processing of the BAL fluid. The aim of the present study was to evaluate a standardized protocol for obtaining, processing, and analyzing BAL fluid and to establish reference values for healthy children. Eighteen children 3 mo to 10 yr of age were lavaged with three 1-ml/kg aliquots of normal saline, using a flexible bronchoscope into the right middle lobe. The first aliquot was processed separately; the second and the third were pooled. There was a higher percentage of neutrophils and epithelial cells in the first aliquot. The number of total cells per milliliter (median, Q1 to Q3) in the first aliquot was 60 (45 to 90) x 10(3)/ml; in the pooled sample it was 155 (75 to 257) x 10(3)/ml. Percentages (median, Q1 to Q3) of different cell types in the pooled sample were: macrophages, 91% (84 to 94); lymphocytes, 7.5% (4.7 to 12.8); neutrophils, 1.7% (0.6 to 3.5); eosinophils, 0.15% (0.0 to 0.3). The ratio of helper/cytotoxic T-cells was 0.58 (0.4 to 1). The results of this study demonstrate that BAL, using a standardized protocol adjusting instilled fluid volume by weight, appears to be appropriate in children and that cellular and protein values from healthy children are, apart from differences in lymphocyte subsets, similar to those found in healthy adults.