This paper describes the results of bursting and deformation tests of brass rotating disks. According to the experiments, the strain-path of a point in a disk was found to be approximately a straight line in the strain-space. Consequently the deformation-theory may be applicable to stress-strain relations in these disks, as well as in the case of aluminium disks. From this point of view, the approximate equation showing the relation between the number. of revolutions and deformation of the hollow disks with a uniform thickness made of a ductile materia1 was proposed, which is more convenient in calculation than those ever proposed. The results of calculations of deformations and bursting speeds for aluminium and brass disks coincide with experimental results fairly well.