A method for studying adsorption-desorption kinetics in porous materials is described. A fixed bed of the adsorbent is challenged with a constant concentration of vapour in an inert carrier and the effluent vapour concentration is monitored as a function of time by using a gas chromatograph. Results obtained with commerciaI filters and nicotine vapour are reported. They fit a mathematical model based on a first-order, reversible rate-controlling process and a linear adsorption isotherm