Bronchoalveolar lavage (BAL) has been used extensively as a research tool to elucidate immunologic events occurring in the lower respiratory tract of patients with numerous diseases and, most recently, to study patients with asthma. We assessed mast-basophiloid cell numbers and histamine levels with a sensitive histamine assay, lower limit of sensitivity, 25 pg/ml, in BAL fluid from normal individuals (n = 9) and compared these results to those obtained from patients with sarcoidosis (n = 31), idiopathic pulmonary fibrosis (IPF) (n = 8), and mild asthma (n = 7). Patients with sarcoidosis demonstrated a significant increase in total BAL mast-basophiloid cells, 9.6 +/- 4.1 X 10(4), compared to total cells in normal individuals, 0.0, p = 0.03, whereas only patients with IPF had significant elevations in BAL histamine levels, 1315 +/- 737 pg/ml, versus levels in normal individuals, 161 +/- 54 pg/ml, p = 0.002. A good correlation existed between histamine levels on an aliquot of lysed BAL cells and BAL histamine levels, R = 0.655 and p = 0.02, but not with either the total number or percent mast-basophiloid cells in BAL assessed on Wright's stained cytocentrifuge preparations. Subjects with asthma had both normal numbers of BAL mast-basophiloid cells and histamine levels. These data suggest that BAL histamine levels are easily quantified, the reason(s) for elevations in BAL histamine levels in IPF need further investigation, BAL histamine levels in subjects with asthma are not elevated in those with mild and stable disease, and lumenal mast-basophiloid cells are one major source of BAL histamine.