The interfacial tension between aluminum and cryolite melts containing different salt additions has been measured by the capillary depression method. The technique is based on the measurement of the capillary depression occurring when the capillary, which is moved vertically down through the molten salt layer, passes through the salt/metal interface. The depression is measured by simultaneous video recording of the immersion height of the alumina capillary. The interfacial tension was found to be strongly dependent on the n(NaF)/n(AlF3) ratio (cryolite ratio, CR). At the cryolite ratio 2.28 (80 wt. % Na3AlF6 + 10 wt. % AlF3 + 10 wt. % Al2O3 // Al, t = 1000 degrees C) the interfacial tension was 546 mN m(-1), while it was 450 mN m(-1) at the cryolite ratio 4.43 (80 wt.% Na3AlF6 + 10 wt.% NaF + 10 wt.% Al2O3 // Al, t = 1000 degrees C). Experiments under current flow conditions were also performed. During the electrolysis the interfacial tension at n(NaF)/n(AlF3) ratio 2.28 decreased from 546 mN m(-1) at zero current to 518 mN m(-1) at 0.112 A cm(-2). The same trend was observed in the system with a cryolite ratio 4.43. The interfacial tension decreased from 450 mN m(-1) at zero current to 400 mN m(-1) at 0.112 A cm(-2). The consequent increase in interfacial tension of these systems caused by interruption of electrolysis was observed. Electrolysis of the system 25 wt.% NaF + 75 wt.% NaCl (eutectic mixture)/Al indicated no influence of applied current on the interfacial tension at 850 degrees C.