Solid cylindrical specimens of Al-4Mg alloy were subjected to in situ compression tests at 550-800 K and at strain rates of 0.02, 0.2, 8, and 200/s. The flow stress, true strain, strain rate, and temperature rise were evaluated from the transient measurements made during the tests. The flow stress values were represented in terms of actual or adiabatic temperature instead of initial test temperature The kinetics of high temperature deformation are expressed by means of some empirical rate equations. Based on the activation parameters, a mechanism of dynamic recovery involving cross-slip of dislocations was identified to be the high temperature rate controlling mechanism in the Al-4Mg alloy.