The mobilization and biodegradation of 13 PAHs sorbed in a creosote-contaminated soil were assessed in the presence of sodium dodecyl sulphate (SDS). In a mobilization experiment, the soil was mixed with SDS solutions (0.005 to 1 % w/v) and the PAH concentrations in the aqueous phase were determined. In a biodegradation experiment, soil residual PAH concentrations were monitored during 45 weeks in the presence of 10, 100 and 500 mg kg−1SDS. The SDS was effective in mobilizing three- and four-ring PAHs. Increasing SDS concentration resulted in the mobilization of very low water-soluble five- and six-ring PAHs. The SDS (100 and- 500 mg kg−4) significantly decreased the biodegradation of fluorene, phenanthrene and all of the four-ring PAHs. PAHs with more than four rings were not biodegraded. The surfactant [α14C]SDS was readily biodegraded. Even if SDS may be efficient in mobilizing PAHs in soil pore water or groundwater, it will not improve PAH biodegradation. Such a result must be considered when using anionic surfactants in the perspective of biological treatment of PAHs.