Heat economy in the Japanese iron and steel industry has made remarkable progress in recent years. In arou nd 1940, an integrated stee l p la nt r eq uired purchased energy equivalent to three tons o f coal for the production of one ton of crude steel. This, h owever, was reduced to 0 .88 tons in 1962 . It is our pleasure to describe in this pape r how su ch a marked progress came to b e attained.