The aim of the present study was to compare cellular and noncellular components of bronchoalveolar lavage fluid (BAL) in a group of children with a diagnosis of chronic diffuse parenchymal lung disease (cDPLD) and a group of children without parenchymal lung disease undergoing BAL for various clinical indications (control group). We evaluated cellular and non-cellular components (total proteins, albumin, hyaluronic acid, and fibronectin) in BAL fluid from 14 children (7 boys and 7 girls; mean age 9.2 years, range 5 months to 18.4 years) fulfilling the clinical and radiological diagnosis of chronic cDPLD, and in 19 controls without evidence of lung disease. The 14 patients were assigned to two study groups: early-stage cDPLD (6 patients; age range 5 months to 5.2 years; duration of illness, 5-7 months) and long-standing cDPLD (8 patients; age range 9.6-18.4 years; duration of illness, 1.2-17.6 years). Ninety-three percent of the patients with cDPLD had at least two BAL constituents outside normal limits, with high numbers of cells, including all types of alveolar cells, but especially lymphocytes and foamy macrophages. These findings indicate a mixed, predominantly lymphocytic alveolitis. Our patients also had a significant increase in two noncellular BAL components, namely fibronectin and hyaluronic acid. BAL samples from children with long-standing cDPLD contained increased numbers of lymphocytes, whereas samples from children with early-stage cDPLD contained increased percentages and numbers of foamy macrophages and increased concentrations of fibronectin, hyaluronic acid, and albumin. In conclusion, we clearly identified an abnormal BAL profile in our group of cDPLD patients. Moreover, BAL findings differentiated younger cDPLD patients in the early stages of their illness from old patients with long-standing disease.