Mesoporous SiO2 was produced by decompn. of Si(OEt)(4), modified with NH2(CH2)(2)Si(OEt)(3) and used for adsorption of theophylline from Me2CHOH/CHCl3 soln. at room temp. The adsorbed theophylline was then released to water or aq. HCl soln. (concn. 0.1 mol/L) at 37 +/- 2 degrees C. The modification of the SiO2 adsorbent resulted in an increase in its adsorption capacity by 60% and a decrease in the theophylline releasing rate.