Although bronchoalveolar lavage (BAL) is useful in studying a variety of lung diseases, it results in substantial dilution of cells and soluble proteins recovered from the lower respiratory tract. Surprisingly little is known about regional differences in BAL recovery in normals and patients with lung disorders. In order to assess regional differences in BAL in normals, we performed a prospective study of BAL in twenty non-smoking volunteers. With the subjects supine, BAL was performed in the right middle lobe (RML), right lower lobe (RLL) and Lingula (LING). The volumes recovered, cell numbers, and angiotensin converting enzyme (ACE) activities were determined separately for each BAL site. ACE was chosen as a representative soluble protein found in the lower respiratory tract which was easily measured in the BAL of normals. BAL volumes recovered from the RLL were significantly smaller than from the RML or LING, perhaps related to the dependent location of the RLL (P = 0.0002). The concentration of ACE and cells recovered per ml of BAL were significantly greater in the RLL than either the RML or LING (P = 0.05). In contrast, the total numbers of cells and total ACE recovered were similar from all sites sampled. This suggests that the differences in measured concentrations were due to different fluid recovery from these sites, resulting in variable dilution of proteins and cells. Urea measurement has been proposed as a means to quantify the epithelial lining fluid (ELF) volume sampled by BAL and estimate the actual concentrations of proteins present in the lower respiratory tract (J Appl Physiol 1986; 60:532-538).(ABSTRACT TRUNCATED AT 250 WORDS)