A dynamic study of the kinetics of theophylline adsorption in aqueous medium by two adsorbent resins is proposed. The adsorption process involves Van der Walls pattern physical bonds. An in vitro haemoperfusion apparatus was schematized and data describing the adsorption-desorption process was obtained. A mathematical treatment led to the conclusion that first-order adsorption and desorption rates are involved, results which led to the consideration of a model of in vivo haemoperfusion in the case of first-order adsorption and desorption, with first-order corporeal elimination. The results indicate that one of the resins used, Amberlite XAD4, already known as a haemocompatible resin, is useful in eliminating theophylline.