A number of studies have found that sources of hydrogen in ESR are water vapors in the mold atmosphere, flux moisture content and hydrogen from the consumable electrode. The ESR process is generally conducted with highly active basic slags capable of absorbing substantial amounts of moisture. It was established [i] that water vapors present in the atmosphere significantly affect the hydrogen content of the ingot. In ESR with flux ANF-7 in an atmosphere saturated with water vapor, the hydrogen content of the ingot reached 16.9 cmS/100 g, compared to 5.9 cma/lO0 g in remelting in an atmosphere of dry argon. Calcining of the flux is very important. Hydrogen content in the ingots increased to 15.2 cma/100 g (5.6 in ESR with calcined flux) with the use of uncalcined flux ANF-6. Since almost no hydrogen is removed during ESR, the initial hydrogen content of the premelted electrode is very important in determining the final hydrogen content of the ingot. According to data published in the literature, in most cases the hydrogen content of the ingot exceeds that of the electrode metal. The possible advantages of the occurrence of chemical reactions in ESR must be emphasized. Film melting of the electrode and the transfer of drops of metal through the slag to the ingot brings the gas-slag--metal system much closer to a state of equilibrium than in any other steelmaking unit.