The group III metal dimers Ga-2 and In-2 and the newly identified intermetallic molecule Gain were investigated in a Knudsen cell-mass spectrometric study of the vapors over gallium-indium alloys. From the all-gas equilibria analyzed by the second-law and third-law methods the following dissociation energies were derived; D-0(0) (Ga-2)=110.8+/-4.9 kJ mol(-1), D-0(0) (In-2)=74.4+/-5.7 kJ mol(-1) D-0(0) (GaIn)=90.7+/-3.7 kJ mol(-1). The value here measured for the dissociation energy of In-2 is discussed and compared with a previous experimental determination and with the results of more recent theoretical investigations.