Combustion in the solid-state displacement reaction between zinc oxide and magnesium during mechanical milling was investigated using X-ray powder diffraction, electron microscopy, and thermal analysis. It was found that mechanical milling decreases the critical reaction temperature at which the combustion reaction occurs. Under the milling conditions employed in this study, the temperature of the powder mixture during ball/powder collisions is estimated to reach a value of 640 K before combustion. © 1993 Academic Press. All rights reserved.