The heats of formation of (U,Mo)Al-3 intermetallic compounds were obtained by measuring the reaction heats of U-Mo/Al dispersion samples by differential scanning calorimetry. Based on literature data for the reaction heats of U3Si/Al and U3Si2/Al dispersion samples, the heats of formation of U(Al,Si)(3) as a function of the Si content were calculated. The heat of formation of (U,Mo)Al-3 becomes less negative as the Mo content increases. Conversely, the heat of formation of U(Al,Si)(3) becomes more negative with increasing Si content. (c) 2006 Elsevier B.V. All rights reserved.