Inhaled urban particulate matter (PM) often contains metals that appear to contribute to its toxicity. These particles first make contact with a thin layer of epithelial lining fluid in the respiratory tract. Antioxidants present in this fluid and in cells might be important susceptibility factors in PM toxicity. We investigated the role of ascorbic acid (C) and glutathione (GSH) as determinants of susceptibility to inhaled residual oil fly ash (ROFA) in guinea pigs (male, Hartley). Guinea pigs were divided into four groups, +C+GSH, +C-GSH, -C+GSH, and -C-GSH, and exposed to clean air or ROFA (< 2.5 micron diameter, 19--25 mg/m(3) nose-only for 2.0 h). C and/or GSH were lowered by either feeding C-depleted diet (1 microg C/kg diet, 2 weeks) and/or by ip injection of a mixture of buthionine-S,R-sulfoximine (2.7 mmol/kg body weight) and diethylmaleate (1.2 mmol/kg, 2 h prior). Nasal lavage (NL) and bronchoalveolar lavage (BAL) fluid and cells were examined at 0 h and 24 h postexposure to ROFA. The C-deficient diet lowered C concentrations in BAL fluid and cells and in NL fluid by 90%, and the GSH-depletion regimen lowered both GSH and C in the BAL fluid and cells by 50%. ROFA deposition was calculated at time 0 from lung Ni levels to be 46 microg/g wet lung. In unexposed animals, the combined deficiency of C and GSH modified the cellular composition of cells recovered in lavage fluid, i.e., the increased number of eosinophils and macrophages in BAL fluid. ROFA inhalation increased lung injury in the -C-GSH group only (evidenced by increased BAL protein, LDH and neutrophils, and decreased BAL macrophages). ROFA exposure decreased C in BAL and NL at 0 h, and increased BAL C and GSH (2- to 4-fold above normal) at 24 h in nondepleted guinea pigs, but had no effect on C and GSH in depleted guinea pigs. Combined deficiency of C and GSH resulted in the highest macrophage and eosinophil counts of any group. GSH depletion was associated with increased BAL protein and LDH, increased numbers of BAL macrophages and eosinophils, and decreased rectal body temperatures. We conclude that combined deficiency of C and GSH increased susceptibility to inhaled ROFA; caused unusual BAL cellular changes; resulted in lower antioxidant concentrations in BAL than were observed with single deficiencies. Antioxidant deficiency may explain increased susceptibility to PM in elderly or diseased populations and may have important implications for extrapolating animal toxicity data to humans.