In these studies, we describe the use of bronchoalveolar lavage (BAL) to study local changes following aerosol bronchoprovocation (BPC) and environmental exposure to antigen in mildly symptomatic asthmatic patients. The BAL was performed in 12 atopic subjects "out of season," and in five normal subjects at baseline, less than or equal to 4, or 24 hours following BPC. Five asthmatic patients were also lavaged during seasonal exposure to allergen. The BAL cells were examined with light and transmission electron microscopy. Bronchoprovocation, by itself, resulted in an average maximal decrease in FEV1 of 13 percent just prior to BAL. There was no significant decrease in FEV1 as a result of BAL. Within four hours after BPC, the number of neutrophils was significantly greater in BAL compared to baseline (1.5 +/- 0.6 X 10(5) vs 3.4 +/- 1.7 X 10(5) cells; p less than 0.01), and the number of eosinophils was significantly greater within four hours and at 24 hours when compared to baseline values (0.4 +/- 0.3 X 10(5) vs 1.9 +/- 0.7 X 10(5) vs 1.2 +/- 0.4 X 10(5) cells; p less than 0.02). Transmission electron micrographs of BAL from lungs of asthmatic patients revealed degranulation of mast cells and loss of core material from eosinophil granules following challenge with aerosolized allergen or with spontaneous environmental exposure. These studies show that in carefully selected, mildly symptomatic asthmatic subjects, BPC and BAL may be useful to evaluate pathogenetic mechanisms in allergic bronchial asthma.