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Serum and tissue homogenates of lung and kidney from 264 mice, half of which had been exposed to continuous or intermittent nitrogen dioxide (NO3 at levels of 0.5 ppm, 0.6 ppm, and 0.8 ppm in three independent experiments, were assayed for intravenously introduced horseradish peroxidase (HRP), a molecular probe for protein leakage. Disc gel elec-trophoresis and enzyme kinetic assays were used independently to quantitate HRP content after 3 and 6 weeks of NO2 exposure, and at 5.5 hr after HRP injection. Of 6 test periods, 5 showed a greater lung HRP content for the NO2, exposed animals by gel scan analysis, and 3 of the 5 increases were statistically significant (p >.05, p >.025, and p >.0025). Similar trends were noted with the HRP kinetic assay. Serum and kidney comparisons showed no consistent differences; 1 of 6 test periods for each was statistically significant. The findings implicate an NO2, induced overload of the bidirectional protein transport system of the lung. [ABSTRACT FROM PUBLISHER]