Bacterial wood decay is a serious threat to the many wooden foundation piles in the Netherlands. In order to learn more about the factors that influence the process of decay, approx. 2000 wood samples taken from Amsterdam piles heads were analysed on type and degree of decay and for 59 extracted piles originated from eight different locations the decay gradient of the pile length was determined. Although large differences in soil constitution (between cities) affect the process of wood decay, on microscale (within Amsterdam), no influence was found that explains the variety in degree of decay at the pile head. Wood quality (growth rate, origin, process of harvesting) is regarded as more important in causing the variety in degree of degradation in pile heads at a similar location. The gradient of bacterial decay over the pile length is mostly decreasing towards the tip and a correlation with soil parameters is suggested.