[en] In 1966 as a consequence of an accident involving two US military aircraft near Palomares two weapons were dropped and their plutonium contents partially scattered. The objective of this paper is to present the most important activities carried out at Palomares in order to characterise the plutonium contaminated site, and to gain further knowledge of the plutonium behaviour in that area. The behaviour of plutonium and americium associated with the soil for more than 30 years has been studied. These studies included chemical and mineralogical investigations of plutonium in the different fractions of the soil, lung solubility of plutonium associated with the breathable fraction, and statistical estimations of the inventory of plutonium remaining in the top first 45 cm of the soil at the most contaminated area in which remediation work was carried out. Other studies focused on the determination of the isotopic relations of plutonium and americium in the surface level. The results show a large variation in plutonium particle sizes in the soil from Palomares. Theoretical calculations estimate that the plutonium remaining in the area could still amount to 16% of the total contents in two bombs. Sequential extraction shows that the highest mobility stage of plutonium represents 0.2% of the total extracted, the remainder (93%) being in the residual fraction. The particles show very low solubility in a simulated lung fluid, and the enhancement factor, defined as the ratio of activity concentration in the inhalable fraction to that in the bulk parent soil was found to be 0.26. (author)