The study evaluated the effect of sulfuric acid aerosol exposure for 2 consecutive days on seven human biochemical blood parameters. A total of 20 human subjects were exposed to 100 micrograms per cu. m. sulfuric acid aerosol for 4 hr/day for 2 consecutive days. A total of 17 human subjects were exposed to 4 hr of ambient air on both exposure days. The chemical blood parameters were measured pre- and post-exposure, and 20 hr after the second exposure: serum glutathione, red blood cell glutathione reductase, red blood cell glucose-6-phosphate dehydrogenase, lysozyme, serum glutamic oxaloacetic acid transaminase, serum vitamin E, and 2,3-diphosphoglycerate. The results indicate no significant response in any of the seven biochemical blood parameters measured. At this level, repeated exposure did not over-burden the upper airway defense against acid aerosol.