The loading of the Superphénix core took place between July 20 and October 3, 1985. The loading of the first core, involving 5.7 tonnes of plutonium, employed a new strategy in the pattern of fuel/dummy assembly replacement moves, known as the checkerboard pattern. This pattern proved highly satisfactory; significant counting rates were obtained on the low-power chambers early in the loading; overall loading time was reduced; and the interpretation of measurements was facilitated., The results were in good agreement with precalculated values, which were reconfirmed by a further, more detailed interpretation that took into account the actual conditions at the time of the reload. The reactivity differences between calculated and measured values for the first critical core loading (containing 33 dummy assemblies) and the fully loaded power core were –0.12 and –0.02% A k/k, respectively. This agreement between experimental and calculated values demonstrates the satisfactory performance of the data sets and methods used in the analysis.