['Eosinophilic lung diseases comprise a group of heterogeneous pulmonary disorders linked by increased eosinophils in bronchoalveolar lavage fluid (BALF). There is supporting evidence that natural killer (NK) cells participate in the regulation of eosinophilic inflammation.', 'Our aim was to investigate the relationship between eosinophils and NK cells in BALF in patients with different interstitial lung diseases (ILDs) focusing on eosinophilic pneumonias.', 'Of 114 patients who presented with increased BALF eosinophils (>5%), 74 patients were classified into the following groups: 27 had eosinophilic pneumonia (EP), 17 had idiopathic pulmonary fibrosis (IPF), 16 had hypersensitivity pneumonitis (HSP) and 14 had cryptogenic organizing pneumonia (COP/BOOP). Total BALF cells, cell density and cell differential counts were assessed and lymphocyte subsets CD3+, CD4+, CD8+, CD19+, CD3-CD16/56+ (NK) and CD3+CD16/56+ (NKT) were determined by flow cytometry.', 'Significant differences were observed in the percentages of lymphocytes (p < 0.001) and CD3+CD16/56+ cells (p = 0.023) among patient groups. In patients with EP, the percentage of eosinophils correlated positively with the number of CD3-CD16/56+ cells (r = 0.522, p = 0.005), the percentage of CD3-CD16/56+ cells (r = 0.690, p < 0.001), and the absolute count of CD3+CD16/56+ absolute cells (r = 0.609, p = 0.001). However, in patients with IPF, HSP or COP/BOOP, no correlation between the percentage of eosinophils and CD3-CD16/56+ or CD3+CD16/56+ cells was observed.'] Are bronchoalveolar lavage fluid eosinophils correlated to natural killer cells in eosinophilic pneumonias?