Bronchoalveolar lavage fluid (BALF) was analysed to obtain information on leakage of proteins from the blood into the respiratory lumen and on local synthesis. Albumin, ceruloplasmin and alpha-2-macroglobulin were measured in paired BALF and serum samples from patients with acute pneumonitis or asthma. Ceruloplasmin (CP) and alpha-2-macroglobulin (A2M) were measured by ELISAs thereby avoiding concentration of BALF. The quotients 10(3) ([protein]BALF)/(protein]serum), Qprotein, were calculated as well as the relative coefficients of excretion, RCE: Qprotein/Qalbumin. The QCP and QA2M increased parallel to Qalbumin in patients with pneumonitis and QCP increased parallel with Qalbumin in the asthma patients. This indicates that abnormal leakage of proteins from the blood rather than local synthesis cause the increased concentrations of these proteins in the BALF. Increased values for the RCE of CP and A2M were observed at normal Qalbumin. We therefore conclude that the determination of CP and A2M yields more detailed information on leakage of proteins from the blood into the airway compartment than that of albumin.