Pifion pine germinating seeds, emergent seedlings, and oneyear-old seedlings were exposed to sulfur dioxide under both acute and chronic exposure conditions. These fumigations were conducted in order to determine the potential for damage to pifion pine in southwestern national parks and monuments where there is potential for exposure to elevated sulfur dioxide concentrations from smelters and power plants. Injury was apparent only in acute fumigations of one-year-old seedlings at ambient sulfur dioxide concentrations of greater than 3 ppm. Chronic fumigations were conducted only at ambient concentrations of 0.2 ppm. Pifion pine resistance was evidenced by lack of effect of fumigation on biomass and growth parameters. Growth rate data for both experimental and control seedlings were fit to a linear growth model with a correlation (r2 = 0.95). The results of this study agree with other data in the literature and indicate that damage from elevated sulfur dioxide concentrations in southwestern national parks and monuments is much more likely for other, more sensitive, species than for pifion pine.