An equation is derived which gives the total energy variation of a ferromagnetic during virgin and cyclic magnetization, and makes possible a detailed analysis of the distribution of energy variation over the various processes involved, and its dependence on magnetizing field and intensity of magnetization. The method is first to calculate for small changes of magnetizing field the total energy made available within the specimen by the current source, by the ordinary magnetocaloric effect and by conversion of magnetic potential energy. From this there are then subtracted the major quantities of energy stored as potential energy: namely, in the demagnetizing and external fields of the specimen, and as magnetocrystalline energy and work done in magnetostriction against internal stresses. Energy changes due to other processes are considered but found to be small.The theory gives calculated curves agreeing well in shape with the observed curves for nickel of Bates and Davis. Discrepancies in magnitude are shown to be largely due to understimation of magnetocrystalline energy. A method is given which, in so far as it is valid, gives a messure of the actual total magnetocrystalline energy and internal work of magnetostriction.It is concluded that the thermal energy curves of Bates and Davis are, in fact, curves of total magnetic and magnetomechanical energy variation.