The lindane sorption-desorption experiments conducted using chitin as an adsorbent in seawater show that the partition coefficients decrease as adsorbent concentration increases and that sorption and desorption are not completely reversible at chitin concentrations lower than 10 g/L. These two effects have been analyzed in terms of a reversible-resistant two-component model of sorptiondesorption. Further studies varying the temperature (from 5 to 45 °C) and salinity (from 15 to 36%o) were carried out to clarify the mechanisms responsible for these effects. The partition coefficients for the resistant and reversible components are found to behave quite regularly in all the experimental conditions: the reversible component is fairly constant in the range of 45 ± 4 L/kg whereas the resistant component partition coefficient is inverse in relation to the chitin concentration, and it approaches zero when the chitin concentration is held at values higher than 10 g/L. The temperature and salinity do not affect the reversible component partition coefficient, and it is shown that the resistant component decreases both as temperature increases and as salinity decreases. Lindane sorption in different types of sites and to differing degrees can account for the observed effects.