Bronchoalveolar lavage (BAL) was performed in 11 basenji greyhound (BG) dogs, which showed persistent airway hyperreactivity to methacholine and citric acid aerosols, and in 15 non-BG dogs, which were significantly less reactive to these challenges. Five of the BG dogs had never received any aerosols prior to BAL, and 3 of the non-BG dogs were allergic to Ascaris suum. No dog received aerosols for 2 wk prior to BAL. Fluid recovered was centrifuged, and aliquots were taken for histamine content and cell identification. Total cell numbers were similar in BG and non-BG dogs. The BG dogs had increased percentages of lymphocytes and metachromatic cells in BAL fluid compared with those in non-BG dogs. Lymphocytes averaged 35.5 +/- 2.3% (mean +/- SEM) and 17.2 +/- 1.2% (p less than 0.005) in BG and non-BG dogs, respectively. The BG dogs that had received previous aerosol challenge and the BG dogs never challenged had 6.2 +/- 0.4% (mean +/- SEM) and 4.6 +/- 0.6% metachromatic cells in BAL. Nonallergic non-BG dogs had 0.91 +/- 0.2% and allergic non-BG dogs had 2.6 +/- 0.5% metachromatic cells in BAL (p less than 0.05 from BG). Total histamine closely correlated with numbers of metachromatic cells in BAL (r = 0.86). Forty-nine percent fewer mast cells were detected in cell preparations fixed in formalin than in cell preparations fixed in basic lead acetate. Electron micrographs revealed 2 mast cell types on the basis of structural characteristics of the granules.(ABSTRACT TRUNCATED AT 250 WORDS)