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Experimental research has been done on a model system that concerns the desorption of polycyclic aromatic hydrocarbons as a limiting factor for the biotechnological sanitation of soil fractions. The system was confinedto the relatively well-degradable napthhalene; this substrate was adsorped as a vapour onto powdered activated carbon by means of a novel method. Increased loading of the adsorbend, or a larger amount of adsorbens present (i.e., an increased rate of naphthalene desorption), had a positive effect on the growth rate. Under nonbiotic conditions, the naphthalene desoprtion rate amounted to, maximally, only 10% of that which was necessary to sustain maximal growth of bacteria under such conditions. From this it was inferred that growth was transfer-limited. In the presence of micro-organisms, the constant of desorption kd had the same value as found in sterile systems (4.8 x 10 -2 m.h -1). Computer simulations based on a mathematical model of growth on adsorbed naphthalene indicated that the process by which naphthalene became available was limited by the rate of desorption.