Research was conducted by the Bureau of Mines to determine the potential for superplastic forming of magnesium-base alloys. The suitability of these alloys for superplastic forming may provide added incentive for the use of domestically available magnesium as a substitute for metals requiring imported raw materials. Commercial compositions of the alloys zk60a (mg-5.5Zn-0.45Zr) and az61a (mg- 6.5Al-1zn) were melted, cast, and extruded to 3/8-inch-diameter rod having average grain diameters of less than 10 um. Tensile testing was conducted at delineate parameters of superplasticity at temperatures ranging from 270 deg to 330 deg c and initial strain rates of 0.002 to 2.0 Min-1. A maximum strain-rate sensitivity index of approximately 0.65 At 310 deg c and 0.002 Min-1 strain rate was determined for az61a, which was not known previously to be superplastic. For zk60a, calculations of experimentally derived data indicated a maximum strain-rate sensitivity index of approximately 0.45 At 310 deg c between 0.04 and 0.1 Min-1 strain rate. Maximum elongations of over 680 pct and 700 pct were obtained for az61a and zk60a, respectively. The potential for commercial superplastic forming would appear somewhat more favorable for zk60a than for az61a, because zk60a retains higher strengths after deformation than does az61a, and maximum superplasticity occurs at higher strain rates in zk600, which facilitates forming.