Technical developments may at any time make it possible to increase the working densities in our electrical machines, and so enable a larger output to be obtained from a given frame-size and weight of active materials. This paper assumes that an increase of transformer flux density is technically feasible, and tries to discover whether it is economically desirable. Only a single situation, and only two (fairly large) sizes of transformer such as would be used on the lower-voltage sections of the Grid, are examined. The results are emphatically against any such increase, and in favour of lower densities than those in use at present.The economics of higher-grade steel is briefly examined.