Induced sputum cell counts provide a relatively noninvasive method to evaluate the presence, type, and degree of inflammation in the airways of the lungs. Their interpretation requires a knowledge of normal values from a healthy population. The objective was to examine the total and differential cell counts in induced sputum from a sample of healthy adults. A total of 118 healthy nonsmoking adults were studied. None had asthma or airflow obstruction (negative history, FEV(1) >/= 80% predicted, ratio of FEV(1) to vital capacity [FEV(1)/VC] >/= 80%, methacholine PC(20) >/= 16 mg/ml). Forty-six were atopic. Sputum induction produced an adequate sample in 96 subjects [53 males, mean age (range) 36 (18 to 60) yr]. The expectorate was processed within 2 h; sputum was selected, treated with dithiothreitol, filtered, and examined in a hemocytometer for total cell count and viability and on Wright-stained cytospins for a differential cell count. The mean, median (90th percentile) total cell count was 4.1, 2.4 (9.7) x 10(6) cells/g and cell viability was 69.6, 72.0 (89.7)%. The proportions of eosinophils were 0.4, 0.0 (1.1)%, neutrophils 37.5, 36.7 (64.0)%, macrophages 58.8, 60.8 (86.1)%, lymphocytes 1.0, 0.5 (2.6)%, metachromatic cells 0.0, 0.0 (0.04)%, and bronchial epithelial cells 1.6, 0.3 (4.4)%, respectively. Female gender and atopy were associated with a significant elevation of eosinophils; mean difference between male/female was 0.3% (p = 0.043) and between atopic/nonatopic 0.4% (p = 0.024). This study has identified reference values for total and differential cell counts in induced sputum of healthy adults.