TiH 2 powder is added as a reactant and pore-forming agent to produce porous NiTi shape-memory alloys (SMAs). The transformation behavior of porous NiTi alloys is investigated because it is relevant to the engineering and medical applications of SMAs. It is found that the transformation behavior of porous NiTi alloys is different from that of cast NiTi alloys. It is demonstrated for the first time, by in situ X-ray diffraction (XRD), that there is no R-phase transformation in porous NiTi alloys, and a broadened, two-peak phenomenon observed with a differential scanning calorimeter (DSC) is not associated with R-phase transformation. The characteristic transformation temperatures of porous NiTi alloys are independent of sintering temperature, sintering time, TiH 2 content, and the heating/cooling rate during thermal cycling between ϩ123 and ϩ423 K. Further, the latent heats of transformation are associated with the TiH 2 content and the sintering conditions.