A fluorimetric method using eriochrome cyanine R (ECR) was applied to determine trace amounts of albumin in bronchoalveolar lavage fluid (BALF). The ECR-albumin adduct showed intense fluorescence and the calibration curve was linear in the range of 2.5-100 microg/ml of human serum albumin (r=0.999). The sensitivity was high enough to determine trace amounts of albumin in BALF. In the present study, the results obtained by the ECR method were compared with those of an EIA, and a good linear correlation was observed between the two methods (r=0.946). The ECR method is simpler and more rapid than EIA. The concentrations of albumin in BALF samples were determined by the ECR method. The albumin level in BALF of healthy nonsmokers (n=9) was lower than that of healthy smokers (n=9) (42.9+/-20.7 and 48.3+/-15.7 microg/ml, respectively). On the other hand, the albumin level of BALF samples obtained from patients with hypersensitivity pneumonitis was increased versus in healthy subjects. The determination of albumin in BALF samples by the ECR method is useful for investigating lung diseases.