The extensive utilization of hydrophobic organic compounds (HOCs) such as pesticides generates high environmental pollution levels. Due to their hydrophobicity, this type of compound tends to accumulate in soil organic matter and, thus, soil desorption limits their availability for microbial degradation. The use of surfactants may increase the pollutant's desorption from the soil. One of the pesticides with strong sorption characteristics is hexachlorocyclohexane (HCH), a mixture of isomers: alpha-, beta-, gamma- and delta-HCH. In this work, we evaluated the use of three surfactants, Triton X100, Tween 80 and sodium dodecyl sulfate (SDS), on the HCH desorption from a sandy loam soil. The effects of the addition of these surfactants on anaerobic biodegradation were studied. To attain this purpose, different assays were performed to evaluate both effects. Triton X100 exerted the best desorption of HCH isomers, followed by Tween 80, whereas SDS caused no significant desorption of the isomers. Triton had a strong inhibitory effect on the HCH biodegradation, while Tween 80 did not decrease the degradation rates of the different isomers. Moreover, the degradation rates of beta- and delta-HCH were significantly enhanced (around 10%). On the other hand, detrimental effects on the biodegradation rates and yields were due to the ageing of the soil, depending on the period of exposure of the soil to the pollutant. (c) 2005 Society of Chemical Industry.