 exposure to air polluted with particles less than 2.5 micron in size is associated epidemiologically with adverse cardiopulmonary health consequences in humans . 
 the goal of this study was to characterize human pulmonary responses to controlled experimental high - dose exposure to fine and ultrafine magnesium oxide particles . 
 we quantified bronchoalveolar lavage ( bal ) cell and cytokine concentrations , pulmonary function , and peripheral blood neutrophil concentrations in six healthy volunteers 18 to 20 hr after inhalation of fine and ultrafine magnesium oxide particles produced from a furnace system model . 
 we compared postexposure studies with control studies from the same six subjects . 
 mean + /- 
 standard deviation ( sd ) cumulative magnesium dose was 4,138 + /- 
 2,163 min x mg / m3 . by weight , 
 28% of fume particles were ultrafine ( < 0.1 micron in diameter ) and over 98% of fume particles were fine ( < 2.5 micron in diameter ) . 
 there were no significant differences in bal inflammatory cell concentrations , bal interleukin ( il)-1 , il-6 , il-8 , tumor necrosis factor , pulmonary function , or peripheral blood neutrophil concentrations postexposure compared with control . 
 our findings suggest that high - dose fine and ultrafine magnesium oxide particle exposure does not produce a measurable pulmonary inflammatory response . 
 these findings are in marked contrast with the well - described pulmonary inflammatory response following zinc oxide particle inhalation . 
 we conclude that fine and ultrafine particle inhalation does not result in toxicity in a generic manner independent of particle composition . 
 our findings support the concept that particle chemical composition , in addition to particle size , is an important determinant of respiratory effects.imagesfigure 1.figure 2 . 
 afigure 2 . 
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