The isothermal ordering kinetics of stoichiometric Ni2Cr was investigated in specimens aged at 500°C and containing 3 different phosphorous impurity concentrations; 0.004, 0.032, and 0.142 atomic percent P. In every case, higher P specimens were found to transform more rapidly than lower P content specimens, with as much as an order of magnitude difference in transformation times. Low and medium P specimens transformed via a continuous ordering process. In contrast, the highest P specimens transformed by an unusual process in which colonies of ordered domains were formed which consumed grains through the advance of an order-disorder interface. Colonies tens of microns in size were typically observed while individual ordered domains were only a few tens of nm in size.