Effect of organic acids on 241 americium and 237 neptunium desorption from an acidic cultivated soil. Naturally occurring organic substances have been recognised as one important factor affecting the behaviour in the environment of transuranic actinides. This experimental study aims at evaluating if some naturally occurring carboxylic acids (vanillic, citric, lactic, oxalic) would affect 241Am or 237Np availability in an acidic agricultural soil. Data show that these acids enhance the desorption of americium and neptunium from the soil, with a noticeable effect of citric acid. The fraction desorbed is multiplied by more than 10 for 0.1 M citric acid, and by 3 or 4 with other acids, in relation with the complexation of radionuclides with these acids. The desorption increases with molar concentration of the acids because of the decrease of pH in acidified soils, except for oxalic acid. The soil moisture conditions seem to affect the desorption results: the percentage desorbed is approximately 10 times lower for batch experiments (saturated conditions) than for centrifugation corresponding to unsaturated soil conditions. These preliminary data are mainly qualitative, but they show that it could be interesting to take into account more realistic physico-chemical conditions when measuring desorption ratios for cultivated soils.