High-strain-rate superplastic behavior of a powder-metallurgy processed 2124 alloy prepared through extrusion at a high ratio of 70 : 1 was investigated. A maximum tensile elongation of 700% was obtained at 823 K and at a strain rate of 10(-2) s(-1). Deformation behavior of this alloy was similar to those reported for other many HSR superplastic materials. Incorporation of threshold stress into the constitutive equation reveals that the true stress exponent is 2 and true activation energy for plastic flow is comparable to that for lattice diffusion in pure aluminum. Comparison of the present alloy with the 2124 Al composite indicates that the composite is weaker than the unreinforced alloy in the temperature range where grain boundary sliding is rate-controlled. (C) 2000 Kluwer Academic Publishers.