The migration and speciation of Cr, Pb, Ni and Cd were investigated in a sewage sludge-amended soil The tests were carried out on samples from the INRA's experimental site at the Station d'Agronomie de Bordeaux, on which varying doses of sewage sludges containing a large amount of heavy metals, in particular Cd and Ni, has been spread (Table 2). The sludge was anaerobically digested, conditioned by heat and dewatered using a filter-press. The soil is gravelly, with a very coarse texture. Table 1 gives the characteristics of this soil. The following treatments were tested (beginning in 1976): T: control, inorganic fertilization only A: application of 10 t ha −1 yr −1 (dry matter) of sludge until 1980. B: application of 100 t ha −1 2 yr −1 (dry matter) of sludge until 1980. The speciation of the metals was investigated by a selective extraction method (Meguellati, 1982) making it possible to divide the samples into five fractions: exchangeable, oxidizable, acid-soluble, reducible and residual. Since metals are generally associated with the fine fraction, the investigation was carried out on the 125 μm fraction samples taken in 1983. The concentration of metals measured in this way (Table 3) show a large increase in the metal contents of the surface horizon. It can be seen that there are large additions of Cd down to the 60–80 cm layer and of Ni down to the 40–60 cm layer in the case of massive applications of sludge. In order to determine the polluted samples with respect to the basic contents of the soil, the metal contents are given as a function of the Al contents (Fig. 1), since Al is representative of the fine and inert phase of the soil (Robbe, 1984). Investigation of the distribution of the metals in the various component phases of the soil using the method of selective extractions may help in understanding the phenomena of migration that have been observed (Table 4, 5, 6 and 7). The metals associated with the exchangeable and oxidizable phases are, in fact, easily mobilized by ion exchange reactions and by the decomposition and transformation of organic matter. In the system studied and over the time period concerned (1976–1983), the following observations have been made: For the four metals studied, Cd is the one that migrates most readily in the soil, down to the 60–80 cm layer. Most of the Cd is in an exchangeable form in the soil, and this relative ease of exchange must be considered in the light of both the great mobility of this metal in soil horizons, of which we have found, and the availability of Cd with respect to plants, which has been reported elsewhere (Juste and Solda, 1985). Ni is associated primarily with the oxidizable phase, and migrated as far as the 40–60 cm layer. Pb is associated with the acid-soluble and reducible phases, and moved little in the soil, as far as the 20–40 cm layer. The additions of Cr were smaller and this metal remains localized in the upper layer. Cr is found primarily in the residual phase. It would therefore seem that the spreading of sewage sludges containing large quantities of heavy metals can contaminate sandy soils down to deep layers, especially in the case of Cd. Moreover, the method of selective extractions provides information about how the metals are bonded to the soil, and may therefore help in predicting their mobility.