In this work, the hydrogen solubility in a titanium aluminium (TiAl) binary alloy melt was investigated through a theoretical analysis and the results compared subsequently with values determined experimentally. Determination of the theoretical values of hydrogen solubility is based on a modified version of Sievert's law, in which hydrogen solubility is related to the activity coefficient of the alloy melt and the hydrogen solubility in pure liquid metals. The activity coefficient is obtained in terms of the free volume theory, in which excess entropy is sufficiently taken into account. The experimental values of the hydrogen solubility in the two alloy melts, Ti45Al and Ti47Al, were determined to validate the calculated values. This was performed using hydrogen charging apparatus. The experimental values obtained were in good agreement with the calculated values. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.