The biological effects of particulate matter (PM) deposition in the airways may depend on aqueousleachable chemical constituents of the particles. The effects of two residual oil fly ash (ROFA) PM samples of equivalent diameters but different metal and sulfate contents on pulmonary responses in Sprague-Dawley rats were investigated. ROFA sample 1 (R1) had approximately twice as much saline-leachable sulfate, nickel, and vanadium, and 40 times as much iron as ROFA sample 2 (R2), while R2 had a 31-fold higher zinc content. Four groups of rats were intratracheally instilled with a suspension of 2.5 mg R2 in 0.3 ml saline (R2), the supernatant of R2 (R2s), the supernatant of 2.5 mg R1 (R1s), or saline only. By 4 days after instillation, 4 of 24 rats treated with R2s or R2 had died, compared with non treated with R1s or saline, and pathological indices were greater in both R2 groups compared with the R1s group. In surviving rats, baseline pulmonary function parameters and airway hyperreactivity to acetylcholine challenge were significantly worse in R2 and R2s groups than in the R1s group. Numbers of bronchoalveolar lavage neutrophils, but not other inflammatory cells or biochemical parameters of lung injury, were greater in both R2 groups compared with the R1s group. These results reinforce the hypothesis that the composition of soluble metals and sulfate leached from ROFA, an emission source particle, is critical in the development of airway hyperreactivity and lung injury.