Pulmonary edema fluid (PEF) and serum (S) were obtained from 14 patients with cardiac pulmonary edema (CPE) and 25 noncardiac pulmonary edema (NCPE) patients. The type of pulmonary edema was based on a clinical classification. The protein content of PEF was not significantly different between CPE (3.89 +/- 0.25 g/dl, mean +/- SEM) and NCPE (4.35 +/- 0.34 g/dl) patients, but the protein content of serum was different (7.18 +/- 0.27 versus 5.13 +/- 0.23, respectively, p less than 0.001). As expected then, the PEF/S ratio was greater in NCPE than in CPE (0.85 +/- 0.06 versus 0.54 +/- 0.03, respectively, p less than 0.05). Thus, differences in the PEF/S ratios in CPE as compared with those in NCPE are independent of mean edema fluid protein content and dependent on differences in serum protein content. PEF and S proteins were separated into 9 fractions of increasing molecular radius by electrophoresis, and fractional concentrations (percent of total protein content) were calculated. The fractional concentrations of these combined fractions of serum proteins were not different between CPE and NCPE. Fractional PEF/S ratios were significantly greater for combined fractions I-III (p less than 0.01) in CPE than in NCPE and significantly less in fractions VII-IX (p less than 0.01). In CPE, a higher percentage of proteins with smaller molecular radii (45 A) enter the airway compartment in part because of higher hydrostatic pressures, whereas in NCPE, larger proteins enter the airways consequent to increased permeability to proteins with molecular radii greater than 72 A.(ABSTRACT TRUNCATED AT 250 WORDS)