Big variations in overall activity and product selectivity in the cyclopentane/deuterium exchange reaction were found in effect of various pretreatments of two chlorine-free Pd/gamma-Al2O3 catalysts. The most important changes are observed when severely prereduced (at 600 degrees C) Pd/Al2O3 catalysts have been reoxidised and mildly rereduced: the multiple type of exchange, typical of mildly pretreated Pd catalysts, is replaced by a stepwise mode, and a big increase in catalytic activity occurs. At this state, the Pd/gamma-Al2O3 catalysts retain some water (as surface hydroxyls) generated by reoxidation and mild reduction. Deuterium spillover from Pd onto alumina and changes in acidity of alumina are invoked to rationalize the kinetic results. Changes in the state of Pd after various pretreatments, as probed by temperature-programmed hydride decomposition, can hardly be correlated with changes in the catalytic behaviour in the exchange reaction.