[en] A novel experimental technique has been developed by which metastable phase transformations in thin films may be investigated. The technique is demonstrated by the determination of the enthalpies of transformation of two commonly observed metastable phases in the compound NiAl₃; the vapor deposited, fcc extended solid solution phase, and the ion-induced amorphous phase. The measured transformation enthalpies are -4.16±0.35 and -5.02±0.49 kcal/mole, respectively. The latter compares with a calculated value of -5.83 kcal/mole, determined using the embedded atom model. This technique demonstrates the feasibility of determining phase transformation enthalpies in ion-irradiated and vapor-deposited metastable phase thin films. (orig.)